This pilot trial will test an intervention (sauna visits) targeting reductions in loneliness in adults aged 19-22 years.

Participants will:

• Visit a sauna in San Francisco once per week for 2 hours by themselves or with a friend, for 8 weeks total
• Complete online surveys throughout their participation

The main question this pilot trial aims to answer are:

• To what extent do participants find the study design acceptable?
• To what extent do participants complete the weekly sauna visits?
• To what extent do participants complete the weekly online surveys?

In the U.S. today, emerging adults (i.e., ages 19 to 22) report high levels of loneliness and social isolation, which are significant risk factors for myriad poor health outcomes. This formative period of emerging adulthood is arguably among the most critical of times: it is when the people who comprise our next generation of leaders have some of their earliest opportunities to build their identities as curious about, accepting of, and open to differences from their peers.

Traditional sauna bathing is a social, mental, and physical health practice associated with greater mental wellness and active social engagement. Recent studies also suggest that thermal therapies, including sauna, may reduce depressive symptoms, which contribute to loneliness and social isolation. Sauna bathing is deeply integrated into the social fabric of several cultures, most notably Finland where it serves as a communal activity that fosters social connection and may help reduce loneliness.

Inclusion Criteria:

• Aged 19-22
• English-speaking
• Able to provide written informed consent
• Graduated from high school or high school equivalent
• Elevated level of loneliness
• Able and willing to receive study text messages
• Able to attend weekly in-person sauna visits in San Francisco, CA

Exclusion Criteria:

• Self-reported heat intolerance
• Pregnancy, active lactation, or intention to become pregnant during the study period
• Regular use of any nicotine products, including cigarettes, vapes, chewing tobacco, or other forms of nicotine (if use is not regular, must be willing to refrain for 24 hours before and 24 hours after sauna visits)
• Current social heat practices 2 or more times per month (e.g., visiting sauna or hot tub facilities with others present)
• Unwilling to refrain from using marijuana products and alcohol for the 24 hours before and 24 hours after sauna visits
• Unwilling to refrain from heavy exercise on the day of sauna visits
• Any medical condition that, in the opinion of investigators, may increase the risk of sauna use or introduce excessive variance into physiological or behavioral responses to sauna visits
• Use of any medication that might impact thermoregulatory capacity or that, in the opinion of investigators, would increase risk of study participation or introduce excessive variance into physiological or behavioral responses to sauna visits

The final IPD dataset will include de-identified self-reported demographic data, self-reported data (e.g., measures of social interaction loneliness), sauna visit completion data, and study assessment completion data.

Beginning 3 months after the publication of results and unending.