Claim Check: "Cold Plunges Boost Immunity"

The claim

"Cold plunges boost your immune system." The claim usually points to fewer colds, faster recovery or stronger defenses. This page separates what was actually measured from what the marketing implies.

What the intervention actually is

"Cold exposure" covers very different things: a cold shower, a swim in cold water, an ice bath and a training program that mixes cold with breathing and meditation. Each has been studied separately, and results do not transfer between them. This page gives no temperatures, times or how-to steps. Safety and practice questions are covered in Cold-Water Immersion: Evidence Summary and Cold and Heat Exposure.

What the evidence shows

• A large randomized trial of cold showers. In the Netherlands, 3,018 adults were randomized to a hot-to-cold shower routine or to a control group. The routine group had 29% less self-reported sickness absence from work, but there was no significant difference in illness days. [1] Participants knew which group they were in, and the outcome was self-reported, so this is a result to take seriously but not as proof of better immunity. Label: promising but limited.
• A small lab experiment. In 24 healthy volunteers (12 trained, 12 not), a 10-day program of meditation, special breathing and cold exposure was followed by a deliberate injection of bacterial endotoxin. The trained group had lower levels of some inflammatory signals and fewer flu-like symptoms. [2] The training also produced short-term changes in blood oxygen and acidity from the breathing method, so the effect cannot be credited to cold alone. [2] Label: promising but limited. A smaller inflammatory reaction to a lab challenge is not the same as better protection against real infections.
• A systematic review. A 2025 meta-analysis of 11 randomized studies (3,177 participants) found no significant effect on immune function measured immediately or one hour after cold-water immersion, but did find a short-term rise in inflammation. The authors noted that the evidence base has few trials, small samples and little diversity. [3] Label: insufficient evidence.
• Surveys of regular plungers. In an online survey of 732 polar plungers and 501 comparison people, plungers reported shorter respiratory infections and shorter sick leave. Benefits appeared to peak at lower plunge frequency, and more frequent plunging was linked to worse results. [4] Self-reported data from people who chose to plunge cannot show that cold caused the difference. Label: mixed.

Plausible mechanisms (separate from the evidence)

Cold-water immersion releases stress hormones, and short-term stress may ready the immune system for injury or infection. That makes an immune effect biologically plausible, but researchers have noted that very few studies have looked at immune markers and actual illness in regular cold-water swimmers. [5] A plausible mechanism is a reason to run trials, not a result.

What the marketing leaves out

• "Immunity" is not a single dial. A change in a blood marker is not proof of fewer infections. See Laboratory Immune Effects vs Clinical Benefit and Claim Check: Boosting Immunity.
• Results from cold showers, cold-water swimmers and training programs are blended together as if they were one thing.
• Exposure doses in studies differ widely, so no figure from one study applies to another.