The study investigates whether repeated exposure to cold showers can improve the ability to cope with and respond to stress. In particular, it examines both the psychophysiological effects of cold showers and the role of expectations regarding their effectiveness. The research adopts a 2×2 experimental design with approximately 120 healthy adults, randomly assigned to either an experimental group or a control group, and further divided based on the presence or absence of information emphasizing the potential benefits of the intervention. The experimental group takes warm or lukewarm showers with a final 30-second exposure to cold water at least four times per week, while the control group takes only warm or lukewarm showers. In parallel, some participants receive positive information about the effectiveness of the intervention for stress management, while others receive no specific information. At baseline and at the end of the study, participants complete questionnaires assessing perceived stress, psychological well-being, and quality of life, along with a physiological measure and a cognitive stress task (Stroop test with heart rate monitoring). During the four-week intervention period, participants keep a daily diary recording shower habits and perceived stress levels.

The study aims to explore the effect of repeated exposure to cold showers on the ability to respond positively to stressful stimuli. The psychophysiological effects of cold showers will be analyzed in combination with expectancy manipulation, which will be emphasized in only one of the two experimental conditions.

The study adopts a 2×2 factorial experimental design. The sample, consisting of approximately 120 healthy adults, will be randomly assigned to either an experimental group or a control group. Within each group, participants will be further subdivided based on the presence or absence of expectancy manipulation regarding the effectiveness of the intervention on stress management. In the experimental group, participants will be instructed to take warm or lukewarm showers at least four times per week at home, with the addition of a final 30-second exposure to cold water. The control group, on the other hand, will be asked to take only warm or lukewarm showers on a daily basis. The second factor considered is expectancy: one group will receive information designed to induce the expectation that this practice may improve stress management, while the other group will receive no specific information. At baseline assessment, participants will complete questionnaires aimed at evaluating psychological well-being, perceived stress, and quality of life. In addition, they will perform a Stroop task with restricted time limits, which is commonly used as a cognitive stressor, while wearing a heart rate monitoring device (Garmin Vivoactive 5). During the intervention phase, which will last four weeks, participants will keep a daily diary to track whether they performed the shower (cold/warm) and their levels of perceived stress. At the end of the intervention, the same measures administered at baseline will be collected again.

Methods and Instruments

The study involves the use of the following questionnaires:

• Demographic data (gender, age)
• Stress (Perceived Stress Scale, PSS-10)
• Resilience (Resilience Scale for Adults, RSA)
• Psychological well-being (Psychological General Well-Being Index, PGWBI-6) All questionnaires will be administered through the Qualtrics platform.

In addition, during the Stroop task, participants will wear a device (Garmin Vivoactive 5) to monitor physiological activation, assessed via heart rate. The psychophysiological data collection protocol includes a 5-minute resting baseline phase and a recording phase during the Stroop task. A visual analogue scale (VAS) measuring perceived stress will be administered both before and after the Stroop task. These assessments will be conducted both at baseline and at the end of the intervention period (i.e., 4 weeks after the initial assessment). During the intervention phase, participants will complete a daily paper diary, self-reported, including:

Time of the shower Approximate water temperature (hot, lukewarm, cold) For participants in the "cold shower" experimental group: compliance with the task (yes/no) Stress VAS ("today was a…" ranging from "very stressful" to "not stressful at all")

Research Procedure

Participants will be recruited through snowball sampling and word of mouth. The invitation will consist of a message such as: "take part in a study on the relationship between daily showering and well-being." After receiving detailed information about the study in person, those who agree to participate will sign an informed consent form. Participants will then be randomly assigned to one of four groups, in line with the 2×2 factorial design.

During the baseline data collection, participants will complete self-report questionnaires. They will then perform a Stroop task, used as a cognitive stressor, while heart rate will be recorded through a wearable device. Perceived stress will also be measured before and after the Stroop task in order to assess the task-induced stress response.

Depending on group allocation, participants will receive the following instructions:

Group 1 - Participants will be asked to end their shower, at least four times per week, at home (or in other locations of their choice), with at least 30 seconds of cold water exposure, preferably very cold. No specific rationale will be provided to support this request.

Group 2 - Participants will be asked to take warm showers at least four times per week, at home or in other locations of their choice. No specific rationale will be provided to support this request.

Group 3 - Participants will be asked to end their shower, at least four times per week, at home (or in other locations of their choice), with at least 30 seconds of cold water exposure, preferably very cold. This request will be supported by an explanation regarding the potential role of cold showers in promoting resilience and reducing stress.

Group 4 - Participants will be asked to take warm showers at least four times per week, at home or in other locations of their choice. This request will be supported by an explanation regarding the potential role of warm showers in promoting resilience and reducing stress.

The intervention phase will last four weeks, during which participants will keep a daily diary to monitor whether they completed the shower (cold/warm) and their levels of perceived stress.

At the end of the intervention, the same measures administered at baseline will be collected again. During the debriefing, the rationale and research design will be explained and, for Groups 3 and 4, informed consent will be requested again (to confirm or withdraw participation following disclosure of the deception).

Study Objectives

The main objective of the study is to investigate the effect of repeated exposure to cold showers on stress responses, assessed through both psychometric and physiological measures. In particular, the study aims to examine whether the inclusion of brief periods of cold water exposure within a daily routine can influence perceived stress levels, psychological well-being, and physiological responses to stress. A further objective is to explore the role of expectancy in the effectiveness of the intervention, by evaluating the extent to which the presence or absence of information about the beneficial effects of the assigned practice may modulate the observed psychological and physiological outcomes. To this end, the study will compare conditions with and without expectancy manipulation in both the experimental and the control groups.

Inclusion Criteria

Participants will be eligible for the study if they meet the following criteria:

• Age ≥ 18 years
• Good general health status, self-reported and/or certified by a medical document (e.g., general medical certificate or sports medical clearance)
• Willingness to participate for the full duration of the study (4 weeks)
• Ability to understand and independently complete questionnaires and study diaries
• Signed informed consent

Exclusion Criteria

Participants will be excluded from the study if they present:

• Uncompensated cardiovascular, neurological, or endocrine conditions considered relevant to stress or cold exposure tolerance
• Medical conditions contraindicating cold exposure (e.g., Raynaud's phenomenon, cold urticaria, etc.)
• Pregnancy
• Use of medications that may interfere with stress responses (e.g., beta-blockers, anxiolytics, systemic corticosteroids)
• Acute or unstable psychiatric disorders
• Inability to comply with the experimental protocol or complete study materials
• Concurrent participation in other studies involving stress or physiological regulation interventions