Cooler temperatures really do put you more at risk for the common cold. The cold virus reproduces more efficiently at cooler temperatures typically found inside the nose than at temperatures that more closely resemble our core body temperature, reports a new study from researchers at Yale University. And that heightened efficiency might be the result of changes in the immune system that occur at cooler temperatures.
The findings might explain "why the cold virus replicates well in the nose."
"The immune defense mechanisms are less efficient in the cooler temperatures," says Akiko Iwasaki, an immunologist at Yale University and a co-author of the study published today in Proceedings of the National Academy of Sciences, "and that can in part explain why the cold virus replicates well in the nose."
In the study, the researchers sampled airway cells from mice capable of becoming infected with the human cold virus. Then, they compared the immune response of these cells at various temperatures. They found that cooler temperatures provide a better breeding ground for the cold virus than warmer ones, mainly because cells at cooler temperatures aren't as good at killing themselves off to prevent further spread of the infection. In a second experiment, the researchers genetically impaired the immune systems of some of the mice. They found that cells from mice with weaker immune systems saw the virus replicate more easily than cells with from mice with normal immune systems — even at higher temperatures. These findings, Iwasaki explains, indicate that "an impairment in the immune responses in the nose can explain, to some extent, why the rhinovirus replicates better in the nose." And temperature appears to have a strong effect on the immune system's response.
wearing a scarf over your nose might be a good move
The link between temperature and the common cold isn’t entirely new. Previous studies found that the cooler temperates found in the nose help the rhinovirus replicate more easily compared with the environmental conditions found in the lungs. But the mechanism behind that phenomenon was unknown. "Studies focused on whether the virus itself worked better at the cooler temperature," Iwasaki says, "but [they] found no evidence for it." The reason they failed to find the result presented in the current study, she says, is because they didn't look at how virus replication is impacted by an impaired immune system.
"Our study asked this question," Iwasaki says, "and found that when we impair the host immune system, the virus does replicate — even at the core body temperature."
Because the study only took place in mice, it’s hard to draw conclusions about human health. A lot more studies, namely those conducted in humans, will have to take place before anyone can address that. In addition, Iwasaki and her team only used one type of cell — airway cells — so the researchers will have to test other immune cells in the future as well. "In the setting of the human infection," Iwasaki says, "we expect that many other cell types will be involved in antiviral defense."
Still, the findings hint that your parents may have been right: wearing a scarf over your nose could actually make a difference when fighting off the common cold. And if covering your nose doesn't actually end up making a difference, at least it will have been slightly warmer for a spell.