Cold Plunging for the Immune System: What the Science Actually Says About Cold Therapy and Immunity

Social media is full of claims about cold plunging and the immune system. Ice baths boost immunity. Cold showers prevent illness. The reality, as usual, is more nuanced — and in some ways, more interesting than the headline version.

The Short, Honest Answer

Regular cold plunging appears to reduce the number of sick days people take, but probably not because you get infected less often. More likely because the illness feels less debilitating and you recover faster.

The science supports: cold therapy can contribute to better immune function, primarily through stress reduction, sleep quality, and sympathetic nervous system adaptation.

The science does not support: cold plunging makes you immune to colds.

The Buijze Study: What 3,018 Participants Tell Us About Cold Plunging and Illness

The most important study on this topic is a Dutch randomised controlled trial by Buijze et al. (2016, PLOS ONE) — one of the largest cold exposure trials ever conducted. 3,018 participants aged 18 to 65 were divided into four groups:

• 30 seconds of cold water at the end of their shower for 30 days
• 60 seconds of cold water
• 90 seconds of cold water
• Control group: warm showers only

After 30 days, the three cold groups were allowed to continue cold showering for a further 60 days at their own discretion.

The Central Finding

The cold showering groups had 29% fewer sickness absence days than the control group (Incident Rate Ratio 0.71, p = 0.003). This is statistically significant and a practically meaningful effect size.

The Critical Nuance

The actual number of illness days was not significantly different between the groups. In other words, the cold showering participants got sick roughly as often as the control group — they just took fewer days off work.

The most plausible interpretation: people who cold shower regularly experience illness as less debilitating. Symptoms may be milder, or the mental resilience built through daily cold exposure makes them more functional when mildly unwell.

One more notable finding: the effects were identical at 30, 60, and 90 seconds. More is not better when it comes to immune benefits.

What "Boosting Your Immune System" Actually Means Scientifically

The phrase "immune system boost" is everywhere in wellness content — and it is scientifically imprecise. The immune system is not a muscle you can simply train up. It is a complex network of cells, organs, and signalling molecules that works best when properly regulated, not when maximally activated.

What the research actually shows is that cold exposure modulates immune regulation — shifting the system towards better balance rather than simply amplifying responses. This distinction matters: an overactive immune system causes inflammation and autoimmune dysfunction, not better health.

How Cold Therapy Affects the Immune System

Sympathetic Nervous System and Inflammatory Response

Kox et al. (2014, PNAS) demonstrated that combining cold exposure with breathing techniques and meditation allowed participants to actively influence their sympathetic nervous system response. The trained group showed fewer inflammatory symptoms and higher adrenaline levels than the control group when exposed to a bacterial endotoxin.

This is the strongest direct evidence that cold exposure can modulate inflammatory responses. An important caveat: the study used the Wim Hof Method — cold plus breathing plus mental training. The effects are not attributable to cold alone.

Stress Reduction as an Immunological Lever

Chronic stress is one of the most consistent drivers of immune dysfunction. Cortisol, the primary stress hormone, suppresses immune activity when chronically elevated. The Cain et al. (2025, PLOS ONE) meta-analysis of 11 randomised trials confirmed that cold water immersion acutely reduces stress. Multiple studies also show that regular cold exposure lowers baseline cortisol reactivity over weeks.

The translation: regular cold plunging reduces stress. Less chronic stress means better immune regulation.

Better Sleep Quality

Sleep deprivation and poor sleep quality are among the strongest predictors of infection susceptibility. Even one night of poor sleep reduces natural killer cell activity. Chauvineau et al. (2021) showed that cold water immersion can deepen sleep architecture and reduce sleep arousals. Better sleep directly supports immune function.

White Blood Cells and Norepinephrine

Šrámek et al. (2000) and Huttunen et al. (2001) documented the sharp hormonal response to cold water immersion: norepinephrine rises by up to 530% and dopamine by up to 250%. Norepinephrine temporarily increases the circulation of white blood cells. Over longer periods of regular cold exposure, this appears to contribute to a mild activation of various immune cell populations.

What Cold Plunging Will Not Do for Your Immune System

Cold therapy is not a protective shield against infection. It will not:

• Prevent you from being exposed to cold or flu viruses
• Replace vaccination, which provides specific immune memory
• Repair an immune system undermined by chronic stress, poor nutrition, or persistent sleep deprivation — at least not on its own
• Substitute for medical treatment during active or serious infections

Should I Cold Plunge When I Am Sick?

With Acute Infection, Fever, or Severe Symptoms: No

Cold exposure strongly activates the sympathetic nervous system and places short-term stress on the body. When your body is already fighting an infection, adding that stress load is counterproductive. Rest and recovery take priority.

With Mild Symptoms and No Fever

Proceed cautiously. Some people feel better after a brief, mild plunge. Others feel worse and extend the illness. When in doubt, skip the session.

During Recovery

Re-enter gradually. Shorter sessions, less cold, less frequent. Your cold tolerance will have reduced during illness. Build back up over a week or two.

Who Benefits Most From Cold Therapy for Immune Support

Not everyone benefits equally. The people most likely to see a meaningful effect:

• People who get ill frequently, particularly when stress and poor sleep are contributing factors
• Professionals in demanding roles where sick days carry high cost
• Parents of young children who are regularly exposed to childhood illnesses
• Athletes during intensive training blocks, when immune function is often temporarily suppressed
• People with frequent travel or shift work schedules that chronically stress sleep and cortisol regulation
• Older adults whose immune efficiency naturally declines with age (with medical clearance)

How to Use Cold Therapy Effectively for Immune Function

Consistency Over Months

The Buijze study's 29% effect appeared after 90 days of regular practice. Occasional cold plunges will not produce this effect. The goal is daily or near-daily cold exposure, especially through the autumn and winter months.

Short Sessions Count

The Buijze study found identical effects at 30, 60, and 90 seconds of cold. For immune purposes, brief, frequent sessions are more valuable than long, infrequent ones. A 2 to 3 minute cold plunge every day beats a 10 minute plunge once a week.

Combine With the Other Immune Levers

Cold therapy works best as part of a broader lifestyle. The most important complementary factors: 7 to 9 hours of sleep, regular exercise, adequate protein and micronutrients, vitamin D supplementation in winter, stress management, and social connection. Cold plunging amplifies these habits; it does not replace them.

Start Before Cold Season

The ideal time to begin an immunity-focused cold routine is before the cold and flu season starts — around September in northern Europe. Allow 4 to 6 weeks to build the habit before you need it most.

Consistency over months is considerably easier to achieve when your ice bath is ready at home any time, rather than depending on a commute to a lake or the weather. The daily practice that produces the Buijze effect requires no friction to maintain.

Frequently Asked Questions

Does cold plunging make you get sick less often?

The largest study on this (Buijze 2016, n = 3,018) showed 29% fewer sick absence days but no significant reduction in actual illness days. Cold plunging may reduce the severity or felt impact of illness rather than the frequency of infection.

Can I cold plunge when I have a cold?

Not with fever or significant symptoms. With mild symptoms and no fever, use careful judgement — and when in doubt, rest. Resume only when fully recovered, starting at reduced intensity.

How quickly does cold therapy work on the immune system?

Measurable effects in the research appear after 30 to 90 days of regular practice. Consistency matters more than intensity here.

Do cold showers work, or does it have to be an ice bath?

The Buijze study demonstrates that brief cold showers produce the 29% sick day reduction. Ice baths produce a stronger physiological stimulus and additional benefits, but for pure immune purposes cold showers are already effective.

Can children cold plunge?

Children have lower thermoregulatory reserve and cool faster than adults. If at all, sessions should be very brief (seconds to one minute maximum), closely supervised, with warm rewarming afterwards. Generally not recommended for children under 12 without paediatric guidance.

What about cold plunging for older adults?

Healthy older adults can benefit, but extra caution applies. Medical clearance is important, especially with cardiovascular conditions, hypertension, or diabetes. Shorter sessions, more moderate temperatures, always with someone present.

The Bottom Line

Cold plunging is not a magic shield against illness. But the evidence supports that regular cold exposure activates several mechanisms associated with better immune function: stress reduction, improved sleep quality, sympathetic nervous system modulation, and — based on the Buijze study — a meaningful reduction in sickness absence.

29% fewer sick days from a 3,018-person randomised controlled trial is one of the strongest single pieces of evidence in cold therapy research. That effect requires consistency over months. Which is significantly easier when your ice bath is ready at home every day.

Ready to build the habit? Explore the Theralpine Rhone with Chiller Pro or Chiller Lite.

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