Folk wisdom has long held that people are more likely to catch a cold in cool-weather or damp conditions but some recent claims have disputed that and found the virus transmits just as often regardless of temperature.  This has been latched onto by people who advocate less energy usage in order to minimize fossil fuel usage.

But the rhinovirus, the most frequent cause of the common cold, can reproduce itself more efficiently in the cooler temperatures found inside the nose than at core body temperature, according to a new study. That means cold is bad. 

The focus of prior studies has been on how body temperature influenced the virus as opposed to the immune system, according to study senior author and Yale professor of immunobiology Akiko Iwasaki, who investigated the relationship between temperature and immune response by examining the cells taken from the airways of mice. They compared the immune response to rhinovirus when cells were incubated at 37 degrees Celsius, or core body temperature, and at the cooler 33 degrees Celsius. 

"We found that the innate immune response to the rhinovirus is impaired at the lower body temperature compared to the core body temperature," Iwasaki said.

The study also strongly suggested that the varying temperatures influenced the immune response rather than the virus itself. Researchers observed viral replication in airway cells from mice with genetic deficiencies in the immune system sensors that detect virus and in the antiviral response. They found that with these immune deficiencies, the virus was able to replicate at the higher temperature.

"That proves it's not just virus intrinsic, but it's the host's response that's the major contributor," Iwasaki explained.

Although the research was conducted on mouse cells, it offers clues that may benefit people, including the roughly 20% of us who harbor rhinovirus in our noses at any given time. "In general, the lower the temperature, it seems the lower the innate immune response to viruses," noted Iwasaki. In other words, the research may give credence to the old wives' tale that people should keep warm, and even cover their noses, to avoid catching colds.

They also hope to apply this insight into how temperature affects immune response to other conditions, such as childhood asthma. While the common cold is no more than a nuisance for many people, it can cause severe breathing problems for children with asthma, noted Ellen Foxman, a postdoctoral fellow in Iwasaki's lab. Future research may probe the immune response to rhinovirus-induced asthma. 

Published in the Proceedings of the National Academy of Sciences. Other authors include James A. Storer, Megan E. Fitzgerald, Bethany R. Wasik, Lin Hou, Hongyu Zhao, Paul E. Turner and Anna Marie Pyle. The research was supported in part by the NIH/National Institute of Allergy and Infectious Diseases under Award U54AI057160 to the Midwest Regional Center of Excellence for Bio- defense and Emerging Infectious Diseases Research, and funding from the NIH (AI054359 and AI064705; to A.I., and T32 HL007974 to E.F.F.), the National Science Foundation (DEB-1021243; to P.E.T.), and NIH Award UL1 TR000142 (to L.H. and H.Z.). A. I. is an investigator of Howard Hughes Medical Institute.