The evidence
What the studies actually say —
including where they are thin.
Moderate evidence for reduced inflammation and short-term mood lift; weaker evidence for the bigger claims. We report study type, sample size, and an effect size we don't inflate.
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Cold Exposure and Systemic Inflammation
Inflammation · 2021Repeated cold immersion lowers circulating inflammatory markers.
A 6-week immersion protocol reduced IL-6 and CRP versus controls, with the effect concentrated in participants who completed at least 80 percent of sessions. The trial was small and unblinded, so we read it as supportive, not settled.
Randomized controlled trial 49 participants Effect strength: Moderate
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Cold Immersion and Immune Markers
Inflammation · 2016Routine cold exposure correlates with fewer self-reported sick days.
A large pragmatic trial found fewer self-reported sick-leave days in the cold-shower group, though sickness severity was unchanged. Self-report and lack of blinding temper the conclusion.
Randomized trial (cold shower arm) 3018 participants Effect strength: Weak to moderate
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Chronic Cold and Inflammatory Cytokines
Inflammation · 2022Sustained cold practice may shift baseline cytokine profiles.
Over twelve weeks, several inflammatory cytokines trended lower in adherent participants. The change was small, variable, and of uncertain clinical meaning; we report individual markers rather than promising an outcome.
Longitudinal biomarker study 54 participants Effect strength: Weak to moderate