Cold Showers: Research Evidence and Physiological Effects
Buijze et al. 2016 RCT (n=3,018): 30-second cold shower finishing routine reduced sick leave by 29% over 90 days. Cold showers do not significantly lower core temperature but strongly activate cutaneous thermoreceptors.
| Measure | Value | Unit | Notes |
|---|---|---|---|
| Sick leave reduction (30s cold finish) | 29 | % | Buijze 2016 RCT, n=3,018; vs control over 90 days |
| Sick day reduction (hot-to-cold routine) | 54 | % (at 90s cold) | Buijze 2016; dose-dependent effect — longer cold exposure, larger reduction |
| Core temperature change | <0.3 | °C | Short cold showers do not meaningfully lower core temperature |
| Skin temperature during cold shower | 15–20 | °C | Depends on shower water temperature and duration |
| Cold shower water temperature (typical) | 10–20 | °C | Cold tap water varies by season and geography; summer tap may be 18–22°C |
| Buijze trial adherence rate | 64 | % | Completed all 90 days; higher in groups with longer cold exposure prescription |
Cold showers are the most accessible form of cold exposure and the only modality tested in a large-scale randomized controlled trial. While they produce different effects than cold water immersion, they have meaningful documented benefits distinct from the ice bath literature.
The Buijze 2016 Trial — Key Data
The landmark study by Buijze, Hopman, and colleagues at the Academic Medical Center Amsterdam is the largest RCT of cold exposure ever conducted:
| Group | Protocol | Sick Leave Reduction | Adherence |
|---|---|---|---|
| Control | Hot shower only | 0% (baseline) | — |
| Cold 30s | Hot + 30s cold finish | 29% fewer sick days | 79% |
| Cold 60s | Hot + 60s cold finish | 54% fewer sick days | 64% |
| Cold 90s | Hot + 90s cold finish | 54% fewer sick days | 58% |
The 90-second group showed no additional benefit over 60 seconds, suggesting a ceiling effect. Longer cold exposure reduced adherence significantly. The 30-second protocol achieved meaningful benefit with highest compliance — a practically important finding.
What Cold Showers Do NOT Do
Cold showers differ from cold water immersion in several important ways:
| Effect | Cold Shower | Ice Bath |
|---|---|---|
| Core temperature drop | Minimal (<0.3°C) | None (standard protocol) |
| Muscle temperature drop | Minimal | 1–4°C in limbs |
| Hydrostatic pressure | None | 1–2 mmHg/cm depth |
| Full surface immersion | Partial (flow pattern) | Full |
| DOMS reduction | Not documented | ~20% |
| BAT activation | Minimal | Significant |
| NE response magnitude | Lower | 200–300% plasma NE |
How Cold Showers Activate Immune Function
The proposed mechanism for sick leave reduction:
- Cold water activates skin thermoreceptors → sympathetic nervous system activation
- NE release → modulation of natural killer (NK) cell activity and granulocyte mobilization
- Repeated NE-immune interaction trains immune readiness
Janský et al. (1996) demonstrated that cold-adapted individuals have higher counts of active NK cells and granulocytes, consistent with immunomodulatory effects. However, the Buijze study measured only self-reported sick days — immune biomarkers were not collected.
Practical Protocol
Based on the Buijze trial (highest adherence, meaningful benefit):
- Shower normally with warm water
- At the end, switch to full cold for 30–60 seconds
- End the shower on cold (do not finish with hot water)
- Practice daily for 90 days minimum before evaluating effect
- No specific time of day is required — morning cold showers are popular but not evidence-based for timing superiority
Related Pages
Sources
- Buijze GA et al. (2016) — The Effect of Cold Showering on Health and Work: A Randomized Controlled Trial. PLOS ONE
- Tipton MJ et al. (2017) — Cold water immersion: kill or cure? Exp Physiol
- Shevchuk NA (2008) — Adapted cold shower as a potential treatment for depression. Med Hypotheses
Frequently Asked Questions
Do cold showers have the same benefits as ice baths?
No — cold showers produce meaningfully different physiological effects. Showers do not immerse the body, so water temperature, surface contact area, and hydrostatic pressure differ substantially from CWI. Core temperature is not lowered by cold showers. The main documented benefit is immune system activation (reduced sick days), not the muscle recovery, BAT thermogenesis, or anti-inflammatory effects seen with full cold water immersion.
What did the Buijze 2016 study actually measure?
The Buijze RCT randomized 3,018 Dutch participants to hot-only showers (control) or hot showers with 30s, 60s, or 90s cold water finish for 90 days. Primary outcome was sick leave from work. Results: 29% reduction in sick days for 30s group; 54% reduction for 90s group. The mechanism is hypothesized to involve norepinephrine release and immune modulation, but the study did not measure biological markers — only self-reported sick leave.
What temperature should a cold shower be?
The Buijze trial used tap water, not temperature-controlled water. Typical cold tap water is 10–20°C depending on season and region. Most of the perceived benefit from cold showers comes from water temperature below ~20°C activating cold thermoreceptors, not from approaching ice-bath temperatures. The physiological threshold for cutaneous cold activation (TRPM8 channels) is approximately 18–25°C.