Effects of Sound Interventions on the Mental Stress Response in Adults: Scoping Review

Introduction

Background

Sound plays a fundamental role in human life, influencing communication, emotional regulation, and environmental awareness. Beyond its basic functions in speech and music, sound can modulate psychological and physiological states [1,2]. Auditory stimuli, including natural sounds, music, and human voices, have been shown to evoke a range of emotional responses and affect stress levels [3]. Recent research has explored the therapeutic potential of sound-based interventions, particularly in managing stress and promoting relaxation [4]. Much evidence documented a sound integrative impact on the psychoemotional and physiological outcomes, making it helpful for treating stress-related conditions such as pain syndromes or anxiety [5-7].

Music and Music Therapy

Sound therapy techniques have gained prominence over the past decades, with a significant emphasis on music as a primary form of sound stimulation. One of the early definitions of music describes it as “humanly organized sound” [8], but there are several alternative perspectives debating this definition [9]. For example, Thaut [10] proposed that music is a complex, time-ordered, and rule-based sensory language. Similar to language, music constitutes a universal part of all human cultures, made up of individual sounds that are structured and layered [11]. The healing effects of music on the mind and body resonate with ancient cross-cultural beliefs [12]. Nowadays, music therapy incorporates various elements of music, such as melody, rhythm, tempo, dynamics, and pitch, along with activities such as songwriting, improvisation, and singing, to promote patients’ physical and mental well-being.

Nonmusical Sound Therapies

Despite the widespread popularity of music, evidence indicates that other sound types, including natural noises, chanting, and speech, can also exert therapeutic effects. For example, listening to poetry has been shown to alleviate symptoms of anxiety and stress [13-15]. Moreover, in various therapeutic frameworks, the quality of communication is often considered a crucial factor. The effectiveness of treatment hinges not only on the specific technique or theoretical knowledge but also on the establishment of a trusting and intimate rapport between the client and the therapist. Ackerman and Hilsenroth [16] indicate that human-rated factors such as warmth, interest, and curiosity, contribute positively to the development of a strong therapeutic alliance. Therapists use different vocal styles depending on the session’s phase, aligning their voices to meet the emotional and therapeutic needs of the interaction [17]. However, distinguishing the impact of content from that of speech acoustics in poetry or therapeutic conversations presents a challenge. A comprehensive understanding of the factors that contribute to the therapeutic influence of sound remains to be elucidated.

Mechanisms of Sound Therapy

The theoretical foundation of how sound interventions can yield therapeutic change and positive outcomes encompasses multiple levels, with the most prominent factor being the learned cognitive response shaped by cultural context [18].

Four-Level Model

Clements-Cortes and Bartel [18] proposed a 4-level model, suggesting that sound can trigger a response due to a set of learned associations that vary from person to person. A particular tone or sound can activate meaningful memories and evoke emotions associated with recalled events [18]. This phenomenon, known as music-evoked autobiographical memory recall, activates related brain networks, potentially inducing shifts in mood and emotional responses [9]. Other responses to sounds are closely linked to our inborn perceptive patterns. Music, characterized by organized vibrations and rhythms, reflects early learned responses. This forms the foundation of our reactions to music—fast music feels exciting, while slow music feels calming. Similarly, louder sounds are associated with strength and boldness, while quieter sounds seem weaker and softer [18].

These principles extend to nonmusical sounds: slower tempo-rhythmical structures, such as a gentle voice or soft breeze, can feel calming, while faster or louder sounds, such as a storm and thunder, can create higher arousal, excitement, or urgency [19,20]. In addition to inborn and early learned responses, situational emotional learning also shapes sound perception. Bliss-Moreau et al [21] demonstrated that voices can gain emotional meaning through past experiences, influencing how quickly participants respond to emotionally charged words based on their previous associations.

Levels 3 and 4 of the model by Clements-Cortes and Bartel [18] encompass responses to sound that are not the result of cognitive processing or learning but rather occur at a vibrational, rhythmic structure. Level 3 focuses on neural oscillatory coherence, where neurons fire in synchrony in response to rhythmic stimulation of the senses (auditory, visual, and tactile), which can lead to various beneficial effects. Level 4 suggests that music and sound can activate mechanisms at the cellular level, potentially influencing everything from neurons to bone and blood cells [18]. Thaut [10] indicates that the brain responds to sound rhythms through involvement, where the listener’s mood aligns with the emotional context conveyed in the sound. This occurs due to acoustic resonance, where the brain naturally synchronizes with the rhythm stimuli [10].

Role of Context and Common Therapeutic Factors

In practical applications, it is crucial to consider collateral factors that influence the perception of sound. The effectiveness of music as an art therapy method also depends on the surrounding environment and common factors applicable across creative therapies. These factors include being present in the moment, experiencing a predictable environment, feeling personally connected, developing social skills, finding meaning, feeling motivated, experiencing emotional release, and being actively engaged. Music therapy enhances therapeutic alliance and group processes through playful interactions, shared experiences, musical attunement, synchronicity, and dialogue. Musical engagement also modulates one’s sense of time and space, fostering a state of flow or providing distraction from stress-inducing thoughts [22]. Another framework for understanding how any therapy, including music therapy, facilitates positive changes is the mediator and moderator model [23,24]. This model considers external factors that affect the strength or direction of the relationship between treatment and the outcome. Moderators may include client or therapist characteristics (eg, gender, ethnicity, and experience), the format of the treatment (individual vs group and in-person vs online), or the treatment frequency (once vs twice a week) [25,26].

Objective and Contribution of This Review

This scoping review aimed to analyze literature on sound interventions targeting stress response and stress-related conditions in adults in laboratory experiments, clinical trials, and randomized controlled trials (RCTs). We also aimed to identify sound interventions that have not been sufficiently studied and require further investigation.

We incorporated investigations focusing on responses of the hypothalamic-pituitary-adrenal axis and the autonomic nervous system as indicators of stress, supplemented by self-reported data and introspective surveys as markers of emotional stress. Our primary outcome of interest is the neural mechanisms underpinning the therapeutic influence of sound. In addition, we are interested in the comparison of delivery methods and sound sample choices for understanding the therapeutic factors of sound for stress reduction.

This study marks a conceptual shift in research of sound therapeutic effects by moving beyond music-focused frameworks to consider nonmusical acoustic interventions using human voices or environmental sounds. This broader perspective opens new possibilities for stress management strategies. By highlighting how diverse sounds can serve for therapeutic changes, this review encourages future studies to explore nonmusical sounds more rigorously and investigate how personal, cultural, or environmental contexts can interact with various sound types.

Moreover, this shift is expanding sound therapeutic potential to services such as classical therapeutic methods that use speech and conversation as primary tools. For instance, it is possible to consider the impact of vocal acoustics, such as tone or rhythm, within psychotherapy sessions to enhance emotional attunement and therapeutic alliance.

In addition, this concept can become a basis for the new technological development. It is possible to bring into the light, track, and analyze vocal elements in real time, allowing therapists to adapt their approach based on the client’s stress markers. Environmental sound tracking also holds potential for improving well-being, as ambient soundscapes could be monitored and adjusted to promote relaxation for everyday environments. This broader perspective encourages innovative approaches that personalize sound to individual needs.

Methods

Overview

This review follows the registered study protocol published in JMIR Research Protocols [27]. The protocol outlines the objective to comprehensively map empirical research on sound interventions for stress reduction. It adheres to Joanna Briggs Institute guidelines and follows the PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews) checklist [28] (Multimedia Appendix 1), with minor adjustments, which will be detailed in the Protocol Adjustments subsection.

The study protocol defines the eligibility criteria for study inclusion, focusing on adult participants, various sound interventions (eg, music, speech, and nature sounds), and stress-related outcomes. The PRISMA-ScR flow diagram (Figure 1) illustrates the study selection process. Guided by the protocol, this scoping review assesses the comparative effects of sound interventions, examines research directions, and identifies methodological challenges in existing literature.

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Research Questions

This scoping review was guided by the population, concept, context framework, recommended for constructing clear objectives and eligibility criteria in scoping reviews [29]. The population, concept, context framework in this study focuses on the population of interest (adults experiencing stress), the concept (therapeutic sound interventions), and the context (various settings in which sound interventions are applied for stress reduction). Through careful refinement, we formulated the following research questions to guide the entire review process:

1. What are the therapeutic factors of sound in the case of reducing stress response and stress-related conditions in human adults? For instance, it might be rhythm, sentiment, environmental context, personal preferences, or background.
2. What are the physiological responses associated with sound interventions in stressful conditions, as measured by biomedical technologies and devices?

Search Strategy and Query String

This scoping review used a systematic search strategy across 4 key medical and interdisciplinary databases: PubMed, Web of Science, Scopus, and PsycINFO (or EBSCOhost). As the neurobiology of music and sound therapy emerged as a separate field in the 1990s, the search strategy covers the research from 1990 till the present day. The search aimed to capture studies addressing the effects of sound interventions, such as music therapy and guided relaxation, on stress reduction in adults. The complete query string formulated for this purpose was as follows: “(stress OR anxiety OR relax*) AND (“sound therapy” OR “music therapy” OR “guided relaxation” OR “guided meditation” OR hypno* OR ASMR OR MBSR) AND (prosody OR song OR poetry OR voice OR paralinguistics OR paralanguage) NOT (children OR infants OR animal OR teen).”

Using the operator “AND” we combined three key fields to comprehensively capture relevant literature (1) mental stress or relaxation indicators: terms such as “stress,” “anxiety,” and “relax*” were included to identify studies focused on both stress-related conditions and relaxation as therapeutic outcomes; (2) sound-based interventions: this field targeted interventions where sound is essential, encompassing “sound therapy,” “music therapy,” “guided relaxation,” “guided meditation,” “hypno*,” “ASMR,” (autonomous sensory meridian response) and “MBSR” (mindfulness-based stress reduction); and (3) voice and paralinguistic elements: we included terms, such as “prosody,” “song,” “poetry,” “voice,” “paralinguistics,” and “paralanguage” to capture studies examining the acoustic characteristics of speech and natural language as therapeutic components. The exclusion criteria were applied using the NOT operator to filter out studies on children, infants, animals, and adolescents, ensuring a focus on adult populations.

This structured approach aimed to capture a comprehensive range of studies, not only focusing explicitly on sound-based therapies but also those involving therapeutic aspects of speech and vocal elements. By broadening the scope in this way, we aimed to explore potential blind spots in sound therapy research, particularly in the therapeutic roles of natural speech and paralinguistic features alongside traditional music-based interventions.

Study Selection

The process of how citations and full-text reports were reviewed, included, and excluded is shown in the PRISMA-ScR flow diagram (Figure 1). The first author, a clinical psychologist, led all aspects of the review, including literature search, extraction, screening, and data analysis. The second author, a psychology researcher, assisted in the literature search and extraction and performed screening independently. Disagreements were resolved through discussion and consensus with other authors of the research consortium.

A 2-step process was followed for study selection. First, we screened citation titles, abstracts, and keywords, classifying each citation as “include,” “exclude,” “unclear,” or “duplicate.” In the second step, full-text reports for citations marked “include” and “unclear” were reviewed to make a final decision on inclusion or exclusion. Reference management and screening were conducted in Rayyan (Rayyan Systems Inc), a web-based app for systematic review management. The inclusion and exclusion criteria are presented in Tables 1 and 2. The inclusion criteria were used to select studies for the review, specifying population, intervention type, outcome measures, study design, and publication type. The exclusion criteria outline conditions under which studies were excluded, including participant characteristics, health conditions, intervention types, and methodological limitations. These criteria ensure a focused review on adult populations using diverse passive sound interventions for stress relief, with an emphasis on studies providing measurable physiological data.

Data Extraction

After initial screening according to the chosen criteria, 2 reviewers independently evaluated the full-text articles. Key information included the following items: (1) authors and year of publication indicating the first author and publication year; (2) country of origin specifying the country where the study was conducted; (3) concept specifying the main idea and hypothesis of the study; (4) population specifying the sample size and population type (eg, nurses, students, and patients with specific diagnoses); (5) study type, for instance, RCTs, clinical trials, or laboratory experiments; (6) intervention type (groups) indicating the type of sound stimulation as described in the article (eg, music, voice, and nature sounds). In most cases, the separation of participants into groups is based on the intervention. This is where we get information about both the types of sound interventions and the participant grouping; (7) outcomes and measurements specifying the target condition or issue that the sound stimulation aims to impact, and how it was measured, including both physiological measures and self-reports of subjective experience (eg, measurements of stress hormones, heart rate variability (HRV), anxiety scale, and emotional state questionnaires); and (8) key findings related to the scoping review questions—indicating the primary results, such as clinical outcomes, body-mind responses, effectiveness, among others.

Thematic Analysis Method

The thematic analysis for this scoping review followed the reflexive thematic analysis framework by Braun and Clarke [30], using an inductive approach to identify key therapeutic factors of sound interventions on stress reduction. The analysis began with a familiarization phase, in which the first 2 authors thoroughly reviewed and familiarized themselves with the data extracted from each included study. This initial stage focused on understanding the study concept and intervention types.

Following familiarization, an open coding process was conducted across the entire dataset, centering on essential elements, such as sound characteristics, and individual outcomes. This coding identified basic elements such as music styles, sentiment, basic physical elements (rhythm and frequency), environmental context, and personal context as core factors within the data. Related codes were then grouped into preliminary categories, organizing the themes based on factors influencing the effectiveness of sound interventions. Three broad categories emerged from this process: (1) sound per se, capturing sound characteristics independent of the listener; (2) personal factors, which focused on listener-dependent characteristics, including musical education, cultural background, personal preferences, and stress history; and (3) environmental factors, covering aspects of sound delivery, such as live versus recorded sound, use of headphones or broadcast sound, and interactions with medical staff or researchers during the session.

Within the category of sound per se, which proved to be the most widely researched, 9 subcategories were developed to reflect specific sound types and qualities. The first 3 of them (1-3) related to music, including different styles, sentiment (such as cheerful vs sad music), and elementary characteristics (such as tempo-rhythm), the next 3 (4-6) outlined nonmusical sounds (eg, white noise, nature sounds, and human voices), and 3 others (7-9) related to the comparison of musical and nonmusical sounds. Initially, the category “environmental context” included subcategories such as “live versus recorded sound” and “presence of supportive personnel,” while “personal preferences” encompassed elements such as “music genre” and “cultural background.” At the same time, due to the modest number of articles assigned to these themes, we decided not to overload the chart and did not include these subcategories in the final edition. In addition, it was important for us to add 3 extra categories for outcomes that were out of the main pattern or for negative outcomes. These were mixed samples (“mix”), relaxing effects of the absence of sound (“0”), and negative, stressful sound effects (“–”).

During the thematic refinement stage, categories and subcategories were iteratively adjusted through regular team discussions and codebook updates, enhancing internal coherence and consistency across the themes. As the thematic map took shape, each category was further refined and defined to ensure clarity and distinctiveness. This thematic framework not only provided a structure for categorizing therapeutic factors and mechanisms of sound interventions but also revealed patterns in the literature and highlighted gaps for future research. As shown in the Results section, some categories have little research, suggesting areas for future studies. We found that in most of the studies reviewed, the hypotheses and groupings were based on the type of sound intervention. This means that the groups typically reflect the type of sound being tested. In some cases, there were >2 types of sounds. If the categorization was unclear or debated, we referred to the study’s concept and research question to identify the primary focus of authors. For instance, if a study had 3 groups, “cheerful music,” “sad music,” and “white noise,” we would place it in the “musical sentiment” subcategory as the study’s focus is on musical emotion rather than comparing music to nonmusical sounds.

Protocol Adjustments

This section outlines the adjustments made during the review process compared to the study protocol [27]. While the overall methodology remained consistent, some procedural differences emerged during implementation. One notable change was the exclusion of gray literature sources, such as Google Scholar, ClinicalTrials.gov, and nonindexed conference proceedings. The final review focused exclusively on peer-reviewed studies to maintain methodological rigor. Many gray literature sources lacked transparency in their methods, making it difficult to assess their reliability. In addition, most did not report detailed physiological stress markers, such as cortisol levels, HRV, or neuroimaging data, which were essential for inclusion in this review. Instead, they often emphasized subjective well-being and relaxation effects, which, while relevant, did not align with the primary focus of this study. Given these challenges, the review prioritized published studies that had undergone formal peer review, ensuring that all findings were based on reliable findings. Despite these adjustments, the core thematic analysis approach, guided by the framework by Braun and Clarke [30], remained unchanged. These refinements ensure that the findings accurately reflect the available evidence while maintaining alignment with the original research objectives.

Results

Overview

The systematic database search obtained 2027 records. After removing duplicates, 1924 records remained for further review. Screening of titles and abstracts led to the exclusion of records that did not meet the chosen criteria, such as unsuitable languages, outcomes, or interventions. Full-text review of the remaining 41 records revealed that 7 did not meet the inclusion criteria due to various reasons, including wrong intervention (n=1, 2%), wrong study design (n=5, 12%) and lack of data on key variables (n=1, 2%). Finally, 34 studies were considered eligible for inclusion in the analysis. These studies were RCTs (22/34, 65%), experiments (9/34, 26%), and pilot studies (3/34, 9%). The search process is outlined in the PRISMA-ScR flowchart (Figure 1). A summary of the included studies, detailing their country of origin, research concept, participant population, and study design is outlined in Table 3.

Thematic Analysis Results

Thematic analysis of the included studies revealed several key factors contributing to the effectiveness of sound interventions. These factors can be categorized into 3 main categories: sound per se, personal factors, and environmental factors (Figure 2).

The majority of the identified articles focused on the characteristics of sound per se (22/34, 65%). For example, studies investigating music interventions often explored different music styles (6/34, 18%), music sentiment (3/34, 9%), and physical aspects such as frequency or tempo (6/34, 18%).

Regarding nonmusical sounds within our predefined inclusion criteria, we found publications comparing musical interventions with a variety of voice-assisted interventions (7/34, 21%). However, no studies were found that focused narrowly on nonmusical sounds for stress relief in adults or compared different sound characteristics beyond the concept of musical intervention.

Within the personal factors category, listener characteristics (3/34, 9%) were identified as influencing intervention outcomes. Environmental factors, such as the way of delivery and context of delivery, were also considered (6/34, 18%).

In addition, the analysis identified a small number of studies (1/34, 3%) that explored mixed samples of sounds and a few that shifted their focus from sound to silence (2/34, 6%) or reported negative effects of sound intervention (3/34, 9%).

Information on key findings for comparing the effectiveness of different sound intervention factors is summarized in Table 4.

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Sound Per Se

Overview

The sound per se category encompasses studies focused on the direct impact of various sound types on psychological and physiological outcomes, independent of personal or environmental factors. This category is divided into subcategories based on music styles, music sentiment, and the physical aspects of music, examining how specific genres, emotional tones, and sound structures influence stress-related markers. Nonmusical sounds were also considered.

Music Styles

In the sound per se—music styles category, studies have consistently shown that different music types can influence relaxation and stress reduction. Umemura and Honda [31] found that classical music reduced HRV, indicating relaxation, while rock and noise had the opposite effect, increasing stress markers. Chafin et al [32] observed that classical music significantly lowered systolic blood pressure following a stress task, while other music styles did not. Labbé et al [33] demonstrated that listening to classical or self-selected relaxing music effectively reduced anxiety and physiological arousal compared to heavy metal or silence. Uğraş et al [34] reported that all music styles reduced preoperative anxiety, with classical Turkish music being the most beneficial. Similarly, Gulnahar and Kupeli [35] showed that Turkish and classical music reduced anxiety during dental procedures more effectively than other styles. Finally, Paszkiel et al [36] found that relaxing music and autonomous sensory meridian response decreased stress levels more quickly than silence, whereas rap music increased stress. These findings highlight the calming effects of classical and relaxing music styles across different contexts.

Music Sentiment

In the sound per se—music sentiment category, research has focused on the impact of different music sentiments on stress recovery. Hirokawa and Ohira [37] suggested that high-uplifting music might enhance mood by increasing norepinephrine levels, while low-uplifting music could potentially boost feelings of well-being. Sokhadze [38] found that both pleasant and sad music improved physiological recovery from stress more effectively than white noise, indicating that positive emotions generated by music might aid in stress recovery. Suda et al [39] demonstrated that major mode music led to lower salivary cortisol levels compared to minor mode music, implying that music in a major mode may induce emotional responses such as happiness, which are closely linked to stress reduction. These findings indicate the potential of music sentiment for stress recovery and mood regulation.

Physical Characteristics of Music

In the sound per se—physical characteristics category, studies investigated how specific musical features or elements affect stress and anxiety outcomes. Wiwatwongwana et al [40] found that binaural beats reduced anxiety and systolic blood pressure more effectively than plain music during cataract surgery. Opartpunyasarn et al [41] showed that binaural beat music significantly reduced anxiety and blood pressure in patients undergoing bronchoscopy. Lee-Harris et al [42] reported that meditative binaural music had comparable effects to calm classical music, with age influencing preferences. Gantt et al [43] found that binaural beat technology reduced stress by altering HRV in military personnel. Calamassi et al [44] demonstrated that listening to 432 Hz music lowered anxiety and improved respiratory rate more effectively than 440 Hz music. Finally, Sharma et al [45] reported that music with tempo or octave changes reduced anxiety and decreased low-frequency brainwaves, reduced default mode network activity, and more balanced brain activity compared to stable music without variations.

Music Versus Human Voice

In the music versus human voice category, studies evaluated the relative effectiveness of music and voice-based interventions on anxiety and physiological responses. Singh et al [46] found that both music and progressive muscle relaxation reduced anxiety and physiological markers in patients with chronic obstructive pulmonary disease, with music showing greater effectiveness. Tang et al [47] reported significant reductions in blood pressure after both audio relaxation and music interventions, with audio relaxation showing a greater impact. Lin et al [48] demonstrated that music therapy was more effective than verbal relaxation or usual care in reducing anxiety and physiological responses in patients with cancer undergoing chemotherapy. Warth et al [50] observed that live music therapy led to greater improvements in vagally mediated HRV compared to a prerecorded mindfulness exercise, highlighting its potential for stress management. Finally, Lee et al [49] found that both music and progressive muscle relaxation improved anxiety and relaxation in patients with cancer, with electroencephalography (EEG) data suggesting different neural mechanisms for each intervention.

Personal Factors

The personal factors category examines how individual characteristics, preferences, and personal involvement influence the effectiveness of sound interventions. Leardi et al [53] found that patients who selected their own music during surgery had lower cortisol levels postoperatively and higher immune function compared to those exposed to standard operating room sounds or new age music. Miller et al [54] showed that joyful music improved endothelial function (flow-mediated dilatation), while anxiety-inducing music decreased flow-mediated dilatation, with the effects comparable to those achieved through exercise or medication. Imbriglio et al [55] reported that guided music listening with relaxing or favorite music reduced muscle effort during awake bruxism episodes in patients with temporomandibular disorders, whereas stressful music increased muscle tension increase. This category highlights the importance of tailored interventions, showing that factors such as personal music selection, emotional connection, and the listener’s psychological state can modulate physiological and emotional outcomes. Studies within this category emphasize that the success of sound-based interventions often depends on aligning the experience with the individual’s preferences and emotional needs.

Environmental Factors

The environmental factors category focuses on the influence of delivery methods and contextual conditions on the effectiveness of sound interventions. This category explores how the medium of delivery (eg, live vs recorded music and broadcast vs headphone playback) and environmental settings (eg, presence of supportive personnel) shape physiological and emotional outcomes. Gelatti et al [56] found that live harp music was more effective than recorded harp music in reducing heart rate and blood pressure during surgery. Bro et al [57] reported a borderline reduction in anxiety with live music during chemotherapy, while prerecorded music showed no significant effect. Lee et al [58] and Kumari et al [59] found that both headphones and broadcast music reduced preoperative anxiety, with no significant difference between the 2 methods, suggesting that broadcast music can be an alternative when headphones are unavailable. Lai et al [60] demonstrated that music interventions with a nurse present improved anxiety, sleep quality, and depression more effectively than recorded music alone. Janelli et al [61] observed no significant changes in the behavior of patients who are restrained and listened to preferred music but noted that patients who were not restrained and listened to music had higher rates of positive behavior. The findings underscore that not only the sound itself but also how and where it is delivered plays a critical role in maximizing the benefits of sound-based interventions.

Mixed Samples

In the mixed samples category, we included only 3% (1/34) of the articles. This intervention is considered mixed because it combines both musical (drumming and music) and voice (shamanic and relaxation guidance) elements represented simultaneously. Gingras et al [64] compared the effects of repetitive drumming with shamanic instructions, relaxation instructions, and instrumental meditation music on cortisol levels and subjective experiences. The study found that all groups showed a decrease in cortisol regardless of the intervention, but repetitive drumming with shamanic instructions led to unique subjective experiences, such as feelings of heaviness and dreamlike states, compared to drumming with relaxation instructions.

Absence of Sound

In the absence of sound category, studies examined the effects of blocking noise compared to music interventions. Kang et al [62] found that blocking noise with earplugs reduced bispectral index scores more effectively than exposure to ambient noise during surgery, while music had no significant difference from noise blocking. This suggests that noise reduction may better aid sedation under noisy conditions. Tsivian et al [63] reported that music with headphones reduced pain perception during prostate biopsy compared to noise-canceling headphones or no intervention. Although anxiety scores remained unchanged, patients in the music group showed smaller increases in diastolic blood pressure, indicating a reduced physiological stress response.

Negative Effects

In the negative category, studies reported increases in stress markers resulting from specific sound interventions. Hirokawa and Ohira [37] found that listening to both high- and low-uplifting music decreased salivary secretory IgA levels, indicating reduced immune function, while silence led to a slight increase in salivary secretory IgA. Imbriglio et al [55] observed that stressful music increased muscle effort during awake bruxism episodes, highlighting the potential for certain music to exacerbate physical stress responses. Paszkiel et al [36] indicated that rap-style music increased stress markers compared to silence. These findings suggest that some sound interventions may have unintended adverse effects on physiological conditions.

Discussion

Principal Findings

This scoping review synthesizes current research on the effects of sound interventions on stress reduction in adults, highlighting key factors that contribute to their therapeutic potential. The analysis revealed that music, particularly self-selected relaxing music, consistently demonstrated a capacity to reduce both physiological and psychological markers of stress. Nonmusical sounds, including nature sounds and prosodic features of human speech, showed promise but were less commonly studied. As for body responses, studies frequently reported positive effects on HRV, blood pressure, cortisol levels, and self-reported anxiety. Furthermore, limited research using brain imaging demonstrated that sound interventions could modulate neural activity associated with emotional regulation, suggesting a neurobiological mechanism underlying the stress-relieving effects. Overall, these findings highlight sound therapy’s potential in stress management and underscore the need for further exploration of diverse sound types and individualized approaches.

Therapeutic Factors of Sounds

The results of this review indicate that sound therapy operates through multiple mechanisms. First, it engages emotional systems to reduce stress. Sentiment, or the emotional tone of the sound, plays a significant role: calming and positive emotional tones, such as those found in soothing music, are frequently associated with reductions in anxiety and stress markers. Tempo-rhythm also emerged as a key factor, with studies showing that slower, steady rhythms often promote relaxation by modulating heart rate and respiratory patterns, while faster tempos can increase arousal. The influence of binaural beats and tempo variations further underscores the importance of this factor in modulating stress responses. These findings align with the 4-level model of sound therapy proposed by Clements-Cortes and Bartel [18], which suggests that sound can impact stress both through learned associations and inherent biological mechanisms.

One key takeaway from this review is the nuanced role of personal factors in determining the effectiveness of sound interventions. Studies where participants were allowed to choose music showed greater stress reduction than those with preselected stimuli. This underscores the importance of individual preferences, emotional involvement, and past experiences in shaping responses to sound therapy. Personalization may thus be crucial in optimizing the therapeutic potential of sound interventions.

While personal preference is often acknowledged as a key factor in stress reduction, deeper cultural influences on sound perception and stress response remain insufficiently studied. As we pointed out earlier at the protocol, some studies focus on country-specific interventions, such as traditional music or poetry, implicitly recognizing cultural context. However, only a few explicitly examine whether the therapeutic effects arise from the sound itself or cultural familiarity and learning [27]. Moreover, the concept of “relaxing” or “soothing” environments is highly context-dependent and shaped by previous exposure, traditional use, and sociocultural meaning. Few studies have examined cross-cultural differences in sound interventions, underscoring the need for research on how various musical, poetic, and speech performance traditions may influence responses across populations.

Environmental factors, such as the method of sound delivery, also play a significant role. Live music therapy, for example, appears to have stronger effects on stress markers than prerecorded music, likely due to the interactive and dynamic nature of live performances. Similarly, interventions that involve a supportive human presence, such as a nurse during a music session, further enhance the therapeutic effect.

We remain cautious about identifying the most effective therapeutic factors in sound therapy due to variability in how studies approach comparisons. Some studies focus on fine-grained distinctions in basic characteristics, such as rhythm or frequency spectrum, while others compare broader intervention clusters, such as music versus guided meditation. This difference in levels of generalization complicates direct comparisons. The reviewed studies provided limited evidence on how nonmusical sounds impact physiological stress. Key therapeutic factors such as tempo-rhythm, sentiment, or frequency, were primarily studied within the framework of music therapy. While it is possible to apply similar analytical frameworks to other sounds, these factors may not fully capture the acoustic characteristics that underlie the psychophysical effects of nonmusical sounds. For example, while rhythm in music typically follows a structured, repetitive pattern, rhythm in spoken voice can be more dynamic and context sensitive. Further research is needed to determine whether these factors contribute to therapeutic effects in both musical and nonmusical sounds, as well as to identify acoustic features specific to nonmusical sounds.

Body Responses to Sounds

The review highlights several physiological responses associated with sound interventions in stressful conditions, measured using various biomedical technologies. HRV and cortisol levels were among the most frequently assessed markers, with multiple studies indicating that calming interventions, such as soothing music or guided relaxation, can balance autonomic nervous system responses, leading to higher HRV and lower cortisol levels. Other commonly measured physiological indicators included blood pressure, electrodermal activity, and respiratory rate, which collectively reflect physiological responses to stress. These metrics were typically recorded using devices such as electrocardiograms for HRV, blood pressure monitors, and salivary samples for cortisol.

In addition, some studies used advanced neuroimaging techniques, such as EEG, to observe brain activity changes in response to sound interventions. This review included limited studies using brain imaging, generally focused on brain activity associated with emotional regulation. For instance, some EEG data showed increased posterior theta and decreased midfrontal beta-2 activity, indicating stress relief. Another study suggested an increase in alpha wave activity, also associated with relaxation, following music and guided relaxation interventions. These neurophysiological findings support the notion that sound therapy can modulate brain activity linked to stress and emotional processing, providing a neurobiological basis for its therapeutic effects.

Identified Research Gaps

Despite these promising findings, several gaps in the literature were identified. There is a clear need for more research on nonmusical sound interventions, particularly human voice–based therapies and natural soundscapes. Studies comparing different types of sound interventions, beyond the binary classification of music versus silence, are limited. In addition, more research is required to understand the negative or side effects of sound interventions and the optimal conditions for their application.

The fragmentation of the research field and reliance on fragmented concepts are also notable. For instance, several studies emphasize the benefits of classical music over other styles, although it remains unclear what specific factors, aside from the researchers’ personal preferences and cultural backgrounds, contribute to the perceived effectiveness of one style over another. Considering the limited investigation into personal factors, future studies could be designed to compare the effects of the same music on both native listeners and foreigners unfamiliar with one or another musical tradition, rather than focusing on comparisons between different regional styles.

Moreover, incorporating an artistic perspective can enhance our understanding of how esthetic and emotional engagement could influence stress relief. Insights from experts in arts and traditional culture may help explain why some sound interventions are more effective than others. Interdisciplinary collaboration between neuroscientists, psychologists, and art experts is essential for bridging scientific and artistic approaches. Future research should integrate physiological stress markers with qualitative methods, fostering a more holistic view of how personal and cultural background could shape the perceptual impact of sound.

In general, individual factors, such as personal preferences, cultural background, and previous exposure to sound therapy, have not been thoroughly examined. Future studies should consider these factors to develop more personalized sound interventions tailored to individual needs.

Another gap is the relative lack of brain imaging studies. There is still limited knowledge about the neural mechanisms underlying sound therapy’s effects. Expanding neuroimaging research in this field could offer deeper insights into how different types of sounds impact neuronal activity related to emotional regulation and stress processing, particularly in real-time applications of sound therapy in stress management.

Strengths and Limitations

One of the key strengths of this scoping review is its comprehensive approach to synthesizing evidence across a variety of sound interventions and stress markers. By including diverse studies, such as RCTs, clinical trials, and laboratory experiments, the review offers a broad perspective on how different types of sound, from music to natural sounds and human voices, can influence stress response in adults. This wide scope provides a valuable foundation for understanding the generalizability of sound interventions in stress management. The review also emphasizes the importance of personal, environmental, and delivery factors, shedding light on the nuances of how sound interacts with different listeners and environments.

Another strength lies in the focus on psychophysiological outcomes. By including studies that measure stress through biomarkers such as HRV, cortisol levels, and blood pressure, alongside self-reported emotional states, the review provides a holistic view of how sound interventions impact both body and mind. This dual focus strengthens the findings by bridging subjective experiences with objective physiological evidence.

However, this review also has some limitations. A key challenge is the considerable variation in study designs, including differences in intervention duration, participant demographics, and measured outcomes. This heterogeneity limits the ability to draw broad conclusions about the effectiveness of sound interventions for stress recovery. Future research should prioritize standardizing intervention protocols, including key design elements such as intervention duration, participant characteristics, and outcome measures. These steps would improve comparability across studies and support future meta-analysis in this field.

Another limitation is our focus on the researchers’ interpretations without direct access to the actual sound samples. As evidenced by data comparison, sound can produce both positive and negative effects, depending on its characteristics. Numerous factors may influence these effects simultaneously. For instance, comparing a heavy metal composition with a Mozart lullaby, it is reasonable to expect differences in style, emotional tone, and frequency spectrum simultaneously. If these compositions were placed in their typical performance contexts, such as a concert hall for the classical music versus a stadium with amplified sound and a large, excited audience for the metal piece, the listening environment would likely impact the physiological response of the listener significantly. Therefore, our framework primarily addresses how current papers conceptualize and investigate sound.

Moreover, the term “classical music” is widely used in the reviewed studies, yet it represents a broad spectrum of musical styles that may evoke diverse responses. While some studies reference well-defined classical works (eg, Mozart or Indian classical music), others use the term more generically, leading to potential inconsistencies in interpretation. As we said before, a major limitation in existing research is the lack of access to original sound samples, making it difficult to assess key acoustic factors such as tempo, instrumentation, or emotional tone. Without standardized reporting, cross-study comparisons remain challenging. A potential direction for future research would be to obtain the sound pieces used in original studies and systematically analyze them.

Finally, the review does not provide insights into the long-term effects of sound interventions, as most studies focus on short-term stress relief. The lack of longitudinal data makes it difficult to assess the sustainability of these interventions over time and their potential cumulative benefits for stress management.

Conclusions

Our scoping review highlights the therapeutic potential of sound interventions in reducing stress, although their effectiveness is influenced by a combination of personal, environmental, and sound-related factors. Future studies should expand the range of sound types studied and explore personalized approaches. Sound-based interventions hold great promise for noninvasive and affordable stress management. Continued exploration of their mechanisms, long-term effects, and optimal applications will be key for unlocking their full potential in both clinical and nonclinical settings.