Peer-Reviewed Research
The Science Behind the Soak
We don't make vague wellness claims. Every benefit on this page is backed by peer-reviewed research from institutions like the University of Eastern Finland, Stanford, UCSF, Harvard, and Mayo Clinic. Here's what decades of science actually says.
Hot Tub Benefits
What Happens When You Soak Every Day
Hot water immersion isn't just relaxing — it triggers measurable physiological changes in your cardiovascular system, nervous system, and immune response.
35%
Lower risk of cardiovascular disease with near-daily hot tub use compared to bathing twice per week or less.
Large epidemiological study published in Heart (BMJ)
36%
Faster sleep onset when soaking 90 minutes before bedtime — confirmed across a meta-analysis of 17 studies.
Haghayegh et al., Sleep Medicine Reviews
22%
Reduction in salivary cortisol (the stress hormone) after a single hot water immersion session.
Current Psychology meta-analysis on hydrotherapy (2024)
Cardiovascular Health
Strong EvidenceHot Tub Use and Cardiovascular Disease Risk
Heart (BMJ) (2020) · Large epidemiological cohort
People who bathed in a hot tub almost daily had a 35% lower risk of developing cardiovascular disease and a 26% lower risk of stroke compared to those bathing twice per week or less.
Daily bathers also showed a 28% lower overall cardiovascular disease risk. The association held after controlling for confounding variables.
Hot Water Immersion and 24-Hour Blood Pressure
Temperature (2025) · Randomized crossover study in hypertensive adults
Both 20-minute and 40-minute immersion at 104°F significantly reduced blood pressure — and the reduction persisted for 24 hours of monitoring.
This is not a temporary effect. The blood pressure benefits last well beyond the soak itself.
Passive Heating and Cardiometabolic Risk
Systematic Review & Meta-Analysis (2025) · Multiple randomized controlled trials
Passive heating interventions (including hot water immersion) produce meaningful improvements in cardiometabolic risk markers, arterial stiffness, and vascular health.
Sleep Quality
Strong EvidenceWarm Water Immersion and Sleep Onset
Sleep Medicine Reviews (2019) · Meta-analysis of 17 studies, 500+ participants
Warm water immersion before bedtime reduces the time it takes to fall asleep by 36%. Optimal timing: soak 90 minutes before your desired bedtime.
Hot water raises your core body temperature. When you exit, the rapid cooling mimics the natural temperature drop that triggers sleepiness — leading to faster sleep onset, deeper sleep stages, and better sleep maintenance.
Real-World Hot Tub Use and Sleep in Older Adults
Sleep Health (2025) · Older adults using hot tubs at home
Confirmed sleep benefits specifically for older adults using hot tubs before bed in real-life settings — not just controlled laboratory conditions.
Pain Relief & Arthritis
Strong EvidenceRheumatoid Arthritis and Hot Water Therapy
Clinical Controlled Study (2018) · RA patients
Standard medical care plus spa/hot water therapy produced significant improvements in joint swelling compared to standard care alone.
The Arthritis Foundation recommends warm water therapy as a complementary treatment for both osteoarthritis and rheumatoid arthritis.
Fibromyalgia and Hydrotherapy
PMC Systematic Review (2020) · Fibromyalgia patients
Just 2-3 weeks of regular hot water therapy reduced fibromyalgia symptoms for up to 6 months. Over 90% of patients reported significant improvements in depression and anxiety alongside physical pain reduction.
Even bathing only twice per week still produced meaningful symptom relief.
Stress & Mental Health
Strong EvidenceHydrotherapy for Anxiety and Depression
Current Psychology (2024) · Meta-analysis
Hot water therapy reduces cortisol production while boosting serotonin and dopamine — with a measured 22% decrease in salivary cortisol after immersion.
Warm Water vs. Exercise for Depression
University of Freiburg (2019) · Adults with depression
People who regularly soaked in warm water experienced greater reductions in depression symptoms than those who relied solely on daily exercise.
Warm water immersion activates the parasympathetic nervous system — directly counteracting the 'fight or flight' response that drives chronic stress.
Sauna Benefits
The Finnish Secret to Longevity
The largest and longest-running sauna study in history followed 2,315 Finnish men for over 20 years. The results changed how the medical community thinks about heat therapy.
40%
Reduction in death from ALL causes with 4-7 sauna sessions per week vs. once per week.
Laukkanen et al., JAMA Internal Medicine (2015)
66%
Lower risk of dementia with frequent sauna use in the same 20-year Finnish study.
Laukkanen et al., Age and Ageing (2017)
63%
Lower risk of sudden cardiac death with 4-7 sessions per week vs. once per week.
Laukkanen et al., JAMA Internal Medicine (2015)
61%
Lower stroke risk with 4-7 sauna sessions per week, even after adjusting for lifestyle factors.
Laukkanen et al., Neurology (2018)
The Finnish Longevity Study
Very Strong EvidenceSauna Bathing and All-Cause Mortality
JAMA Internal Medicine (2015) · 2,315 men, 42-60 years old, followed for 20.7 years
Men who used the sauna 4-7 times per week had a 40% reduction in death from all causes compared to once-per-week users. Risk of sudden cardiac death was 63% lower.
This is one of the largest protective effects observed for any single lifestyle intervention. The dose-response relationship (more sauna = better outcomes) strengthens the causal argument. Study parameters: ~174°F for ~20 minutes per session.
Expanded Cohort: Men and Women
BMC Medicine (2018) · 1,688 men and women
Follow-up study confirmed that sauna bathing is associated with reduced cardiovascular mortality and improves risk prediction in both sexes — not just men.
Brain Health & Dementia Prevention
Strong EvidenceSauna Use and Dementia Risk
Age and Ageing (2017) · 2,315 men followed for 20.7 years
Sauna use of 4-7 times per week was associated with a 66% lower risk of dementia and a 65% lower risk of Alzheimer's disease. Even 2-3 sessions per week showed a 20% risk reduction.
Expanded Dementia Cohort
Alzheimer's Drug Discovery Foundation Review (2023) · 13,994 men and women, followed for up to 39 years
Those using the sauna 9-12 times per month had a 21% lower risk of dementia compared to those using it 0-4 times per month.
Proposed mechanisms include improved vascular function, reduced inflammation, lower blood pressure, and heat shock proteins that may help clear misfolded proteins associated with neurodegenerative diseases.
Mental Health & Depression
Strong EvidenceWhole-Body Hyperthermia for Major Depression
UCSF Osher Center (HEATBed Trial) (2024) · Randomized controlled trial, 12 completers
After whole-body heating to raise core temperature to ~101.3°F, 11 of 12 participants no longer met the diagnostic criteria for major depressive disorder at post-treatment.
People with depression tend to have higher core body temperatures. After whole-body heating, the body's subsequent cooling may have an antidepressant effect. Heat also triggers the release of endorphins and serotonin.
Skin Health
Moderate EvidenceInfrared Radiation and Skin Rejuvenation
Annals of Dermatology (2020) · 20 patients, 6-month clinical trial
Regular infrared sauna use produced 51-75% improvements in skin texture, with biopsies confirming elevated collagen and elastin levels. Separate studies showed 20-50% improvement in wrinkles, skin texture, and tone.
Heat increases blood circulation to the skin, delivering more oxygen and nutrients, and stimulating fibroblast activity — the cells that produce collagen and elastin.
Swim Spa Benefits
Why Water Changes Everything About Exercise
The physics of water make it the ideal exercise environment — more resistance, less impact, and results backed by decades of rehabilitation science and systematic reviews.
12x
More resistance than air — every movement in water is a strength-building exercise.
Exercise physiology established data
50-90%
Body weight reduction from water buoyancy, depending on depth — dramatically reducing joint stress.
American Council on Exercise
400-600
Calories burned per hour of water aerobics — comparable to cycling or brisk walking, with a fraction of the joint impact.
Exercise physiology data
Rehabilitation & Pain Relief
Very Strong EvidenceAquatic Exercise for Osteoarthritis in Older Adults
Systematic Review of 12 Randomized Controlled Studies (2025) · Adults over 60 with osteoarthritis
Aquatic exercise significantly improved balance, stiffness, pain, and walking ability compared to non-exercise controls. Critically, aquatic exercise relieved pain better than land-based exercise.
Warm pool water relaxes muscles and nerve endings, providing superior pain relief. Participants showed significant improvements in step length and stride length — critical metrics for fall prevention in elderly populations.
Water Exercise and Chronic Pain
Journal of Exercise Rehabilitation (2021) · Chronic pain patients
Just two hour-long water exercise sessions per week reduced pain intensity and improved personal care, sitting, standing, and sleeping ability.
Aging & Fall Prevention
Very Strong EvidenceAquatic Training for Elderly Balance and Strength
International Journal of Clinical Practice (2025) · Randomized controlled trial, elderly men
A 3-month aquatic training program produced significant improvements in static balance, dynamic balance, upper and lower body flexibility, and muscular strength.
Falls are the #1 cause of injury death in adults over 65 (CDC). Aquatic exercise improves both static and dynamic balance in a controlled, private environment — no fear of falling on hard surfaces.
Cold Plunge Benefits
What Two Minutes of Cold Can Do
Cold water immersion triggers one of the most powerful neurochemical responses available without a prescription. The science explains why people who cold plunge say they feel like a different person afterward.
250%
Increase in dopamine — the motivation molecule — from cold water immersion. The effect lasts for hours, not minutes.
European Journal of Applied Physiology; Huberman Lab analysis
530%
Increase in norepinephrine, driving energy, alertness, and focus after cold exposure.
Clinical catecholamine studies
11 min/week
Total cold exposure needed for health benefits — broken into 2-4 sessions of 1-5 minutes each.
Dr. Andrew Huberman protocol, Stanford
The Dopamine & Neurochemistry Response
Strong EvidenceCold Water Immersion and Catecholamines
European Journal of Applied Physiology (2000)
Cold water immersion at 57°F produces up to a 250% increase in dopamine and a 530% increase in norepinephrine. Unlike stimulant drugs that cause a sharp spike and crash, cold exposure produces a gradual, sustained elevation lasting several hours.
Dopamine is the 'motivation molecule' — low dopamine is associated with depression, lack of drive, and inability to focus. A single cold plunge session can shift your entire neurochemical state for hours.
Athletic Recovery
Strong EvidenceCold Water Immersion for Exercise Recovery
Sports Medicine (2022) · Systematic review and meta-analysis
Cold water immersion is an effective recovery tool after high-intensity exercise — with moderate reductions in delayed-onset muscle soreness (DOMS) and reduced creatine kinase (a marker of muscle damage) at 24 hours.
Optimal Cold Immersion Protocol
Frontiers in Physiology (2025) · Network meta-analysis
Optimal protocol: 10-15 minutes at 41-50°F for biochemical recovery, 10-15 minutes at 52-59°F for muscle soreness relief. Immersion immediately after exercise provides the greatest benefit.
Immune Function
Moderate EvidenceCold Showers and Sick Days
Dutch Cold Shower Study (2016) · Large population study
People who took daily cold showers showed a 29% reduction in self-reported sickness absence from work.
The Wim Hof Method and Immune Response
PNAS (Proceedings of the National Academy of Sciences) (2014) · Controlled trial, 12 trained men vs. controls
After just 4 days of training, subjects could suppress their innate immune response to injected bacterial endotoxin — showing fewer inflammatory proteins and recovering faster than controls.
Note: The Wim Hof Method combines cold exposure with specific breathing techniques. The immune effects may come from the combination, not cold alone.
Mental Resilience
Moderate EvidenceCold Water Immersion and Mental Wellbeing
PLOS ONE (2025) · Systematic review, 11 studies, 3,177 participants
Multiple studies show mood improvements immediately after and 30 minutes after cold water immersion, with significant improvements in self-esteem and depression ratings. Repeated exposure may decrease cortisol response over time, indicating adaptive stress resilience.
This is called the 'cross-adaptation hypothesis': training your stress response in the cold may make you more resilient to stress everywhere else in life.
Contrast Therapy
Why Hot + Cold Is Better Than Either Alone
Alternating between heat and cold creates a “vascular pump” effect that dramatically improves circulation, accelerates waste removal, and delivers nutrients to damaged tissue. This is the protocol used by professional athletic teams worldwide.
23%
Reduction in delayed-onset muscle soreness using contrast therapy vs. passive recovery.
Journal of Strength and Conditioning Research
3 min / 2 min
The protocol: 3-minute hot phase (100-104°F) followed by a 2-minute cold phase (50-59°F), repeated 2-3 times.
Randomized trials, Journal of Strength and Conditioning Research
Contrast Therapy for Musculoskeletal Pain
PMC Scoping Review (2025)
Confirmed mechanisms and efficacy: cold reduces cytokine production and COX enzyme activity (anti-inflammatory), while heat promotes tissue repair through collagen synthesis. The combination resolves inflammation AND promotes regeneration simultaneously.
Enhanced Circulation and Recovery
Journal of Strength and Conditioning Research (2022) · Randomized trials
3-minute hot / 2-minute cold cycles produced enhanced circulation, reduced swelling, faster lactate clearance, and fewer muscle microtears compared to passive recovery.
Recommended Contrast Therapy Protocol
Heat Phase
3-4 minutes
100-104°F (hot tub or sauna)
Cold Phase
1-2 minutes
50-59°F (cold plunge)
Cycles
2-3 rounds
15-20 minutes total
Key Rule
End on cold
Maximizes catecholamine response
Experience the Benefits in Person
The research is compelling. But the best way to understand what a hot tub, sauna, swim spa, or cold plunge can do for you is to try one. Visit our showroom — no pressure, just warm water and honest answers.
Medical Disclaimer: The information on this page is for educational purposes only and is not intended as medical advice. The studies cited describe statistical associations and clinical findings — individual results vary. Always consult your physician before beginning any new wellness routine, especially if you have cardiovascular conditions, are pregnant, or take medications affected by heat or cold exposure.