Does cold showering boost your immune system?

Cold showering or cold immersion causes a temporary spike in inflammatory markers in your blood immediately afterwards. This is a normal stress response from the body, not a sign that your immune system is improving. The spike then subsides.

There is hardly any evidence for a direct effect on your immune system. A large analysis of eleven studies involving more than three thousand participants found no measurable effect on immune markers immediately after cold exposure. There was an indication that people who take cold showers had 29% less sick leave, but that finding is based on very few studies with small groups, so no conclusions can yet be drawn from it.

Six weeks of cold immersion three times a week showed a small activation of certain immune cells in young, athletic men. However, most of the measured immune values did not change, and what that small change means in practice is unclear.

Cold immersion combined with meditation and special breathing techniques appears to reduce the inflammatory response to an experimental bacterial infection. But in that study three techniques were applied simultaneously, so cold alone cannot be identified as the sole cause.

People who report having fewer and shorter colds as a result of cold showering are known mainly from questionnaire studies in which people sign up voluntarily. Those people are probably healthier or live more healthily in general. It has also been established so far that a brief cold immersion does not make you acutely ill, but evidence that it builds up your resistance is lacking.