Why Does the Immune System Struggle When the Weather Changes?
The immune system protects the body against invading pathogens, cancer, and allergens. However, some people may notice that these defenses perform slightly under par when the seasons change. Why does the immune system appear to go on the fritz when the weather shifts?
Sharon Evans studies the mechanisms, including fever, that influence T cell trafficking across blood vessels.
Roswell Park Comprehensive Cancer Center
Sharon Evansa cancer immunologist at Roswell Park Comprehensive Cancer Center who studies the role of temperature in T cell responses, said that, to date, the influence of the external environment on immune function is understudied. However, researchers have found that internal temperature affects cell activity. For instance, heat in the form of low-grade fevers activates many T cells and other immune mediators.1
“The other aspect is, it depends on what temperature you’re at,” Evans said. Previous studies showed that people living in warmer temperatures had better survival rates for breast cancer, whereas cold conditions repressed immune responses in mice.2,3
Thus, besides fever activating the immune system, Evans said that warmer environments promote better immune responses because less energy is diverted to regulating the body’s temperature. Maintaining this homeostasis is crucial for the proper functioning of the human body. “The body will expend a lot of energy on that at the expense of other factors, including the immune system.”
Based on this knowledge, Evans hypothesized that at colder temperatures, more resources are shuttled toward homeostasis, leaving less fuel available for immune cells. “Generally, the cold temperatures are anti-inflammatory. The immune response just doesn’t work as well and, molecularly, the adhesive interactions just don’t really bind as well,” she said.
Seasonal shifts also bring changes in humidity and wind, which can affect the skin and mucosal barriers, and in turn, the immune response, according to Evans. Drier conditions can lead to more pathogens or other irritants entering the body, driving inflammatory responses. In contrast, excessive humidity can reduce the evaporation of sweat, thus preventing the body from being able to cool itself.
Evans remarked, though, that probably the biggest effects seasonal changes bring to the immune system are those of people’s behavior. Cold temperatures drive people indoors, where pathogens spread more easily. Meanwhile, warm days draw individuals outside, where people can be exposed to pollutants and allergens, which Evans said can render immune responses less prepared to fight actual infections.
However, as global temperatures rise and expose people to extreme heat and weather, these environmental effects may become more relevant. “It’s going to be challenging to see how this all shakes out in terms of the impact on the immune system,” Evans said. “We just don’t know the answer yet.”
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