Does cold exposure boost immune function?

What does the evidence actually show about cold exposure and immunity?

The answer is not a simple yes or no. Cold exposure triggers a range of physiological responses, and its effect on the immune system depends heavily on the context. In healthy adults, repeated whole-body cryotherapy at -90°C for 9 weeks led to measurable immune modulation, including a significant increase in lymphocytes (from 25.6% to 29.3% of white blood cells) and a decrease in granulocytes (from 63.5% to 58.7%), along with a marked rise in the anti-inflammatory cytokine IL-10 (from 33.5 to 63.5 pg/mL) [1]. This suggests a shift toward a more regulated, less inflammatory immune state.

Similarly, a study on healthy adults taking daily cold showers for 90 days found significant increases in immunoglobulins (antibodies) and the cytokines IL-2 and IL-4, which are crucial for T-cell activity and antibody production [10]. In contrast, the hot shower group showed a significant decrease in IgM antibodies at 60 and 90 days [10]. This indicates that regular, brief cold exposure may prime the adaptive immune system.

However, the picture is different for acute or extreme cold. In mice exposed to 4°C, cold exposure elevated plasma IgG levels but reduced the ability to clear bacteria, a sign of immunosuppression [4]. In fish, cold stress suppressed the expression of key immune genes and reduced chromatin accessibility at immune-related transcription factors, impairing antibacterial defense [8]. These findings highlight that the immune system's response to cold is not uniformly positive.

Who benefits from cold exposure, and who might be at risk?

The benefits of cold exposure for immune function appear most pronounced in healthy individuals who are not under significant thermal stress. For example, healthy adults who took regular cold showers showed enhanced humoral and cell-mediated immunity [10]. Similarly, preschool children who underwent cold conditioning (cold dousing) showed increased interleukin-6 levels, but all values stayed within normal range, suggesting adaptation without a stress response [7]. This implies that for generally healthy people, controlled cold exposure can be a safe way to stimulate immune activity.

In contrast, for individuals with pre-existing conditions like asthma, cold exposure can be problematic. A study on asthma patients found that cold air hyperventilation triggered a Th1-dominant immune response, with increased pro-inflammatory cytokines (TNFα, IL-2, IL-1β, IL-6) and IFN-γ, which was associated with cold-induced bronchospasm [5]. This suggests that for people with respiratory conditions, cold exposure may exacerbate inflammation rather than boost immunity.

Additionally, the type of cold exposure matters. In laying hens exposed to heat stress, providing cold drinking water helped restore suppressed immune function, including increasing B-cell and helper T-cell counts and boosting IL-2 and IFN-γ levels [3]. This shows that cold can be therapeutic when the body is already under heat stress, but the same may not apply when the body is already cold-stressed.

How does cold exposure actually affect the immune system?

Cold exposure influences the immune system through several pathways. One key mechanism involves the activation of cold-sensitive ion channels in the skin, such as TRPM8. In rats, pharmacological activation of TRPM8 (the same channel triggered by menthol or cold) doubled antigen binding in the spleen and significantly reduced blood IgG levels [6]. This suggests that skin cooling alone can directly modulate immune responses, independent of core body temperature changes.

Another mechanism is through the upregulation of genes involved in cytotoxicity. In a human study, mild cold exposure (about 2.5 hours) acutely increased mRNA levels of GNLY and PRF1, which encode proteins that help immune cells kill infected or cancerous cells, by 35% and 45%, respectively [2]. This indicates that even mild cold can prime the immune system for a more aggressive response to pathogens.

Cold exposure also affects the tumor microenvironment. In a mouse model of breast cancer, cold-water swimming combined with chemotherapy enhanced antitumor immunity, increasing IL-2 and IFN-γ levels while reducing pro-inflammatory IL-6 and TNF-α [9]. This suggests that cold can help turn an immunosuppressive tumor environment into one that is more responsive to therapy. However, the same study also showed that cold exposure alone (without chemotherapy) had a tumor-free rate of 60%, compared to 0% in controls, indicating a direct immune-boosting effect [9].

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