Conventional knowledge informs us that the onset of winter and cooler weather brings forth an inundation of flu cases. Blocked noses, sore throats and incessant coughing are among the common symptoms for those unfortunate enough to fall ill to the common cold, also known as the rhinovirus. With the frequent development of runny noses in cold environments, the association between cold weather and the common cold was bound to happen. The truth behind whether this illness rears its head more prominently during wintertime, however, is very much up for debate.

Trench warfare in World War I exposed soldiers to lengthy periods of time in cold and wet conditions. Soldiers who were continuously exposed for three days were four times likelier to develop a cold than their warmer comrades [1]. Yet, those that live north of the Arctic Circle are no more likely to develop colds than Australians [2]. Even Benjamin Franklin added his own two cents to the debate, noting that soldiers who constantly wore wet clothing did not necessarily contract the cold [3].

Initial efforts to discover the cause of the cold began with Walter Kruse in January 1914. When one of his colleagues showed up to work with a cold, Kruse took samples of his nasal secretions and diluted them fifteen-fold with saline. He then passed the mixture through a fine ceramic Berkfeld filter to remove any bacteria (viruses are often much smaller in size than bacteria and would therefore pass through). Kruse gave samples to twelve of his colleagues to inhale and four of them developed colds after incubation for 1-3 days (talk about team spirit). The crude experiment proved that the cold was not caused by bacteria, but by a virus [4]. While this information seems archaic compared to what we know today, whether viruses really caused sickness went unanswered at the time. Further experimentation seemed necessary.

Chimpanzees were purported to catch colds from their zookeepers, making them ideal test subjects. Chimps that were kept in isolation from one another were given bacteria-free filtrates of nasal secretions from humans who had contracted the common cold. These chimps developed human-like symptoms of the cold. Test subjects that were given filtered nasal secretions from healthy humans did not, confirming the hypothesis that a virus was indeed responsible for colds and was, in fact, contagious [5]. It wasn’t until 1956 that the cold virus was isolated and cultivated. Two competing strains were discovered in the same year and appeared to possess slightly different characteristics. Both, however, induced mild respiratory symptoms that indicated a cold [6].

One of the first studies which challenged the convention that cold temperatures induce increased susceptibility to the development of a cold, appeared in 1968. The experiment involved 44 American male prisoners. The newly discovered cold virus was dripped into the noses of 27 “volunteers” (the question of ethics for this experiment perhaps warrants an article on its own). They were then subjected to temperature conditions of either 4 °C or 32°C during infection, incubation, peak of illness and recovery. The authors concluded “no significant differences” regarding the probability and severity of infection between those deliberately infected and the control group [7].

Despite the evidence, the jury is still out. Cold temperatures constrict blood vessels in the nasal canal to maintain body temperature. Vasoconstriction drives defensive mucus in the nasal passage, which is designed to trap pathogens, lowering respiratory defenses [8]. Should breathing take place through the mouth instead of the nose, these preliminary defenses are bypassed entirely. Low humidity, a hallmark of winter season, also expedites the travel of infected mucus droplets in the air. The lower the humidity, the more rapidly water evaporates, creating a more streamlined projectile with a greater lingering period.

One popular school of thought suggests that cold weather motivates people to congregate in close indoor quarters. Proximity to the sick accelerates contagions, and recycled indoor air exacerbates this situation. The theory seems to account for the prevalence of the common cold during colder weather.

Most scientists would agree that cold weather itself does not cause a cold, but that the cold is caused by a collection of rhinoviruses, each having its own virility in cold temperatures and the other conditions that accompany winter weather. Our habits in cold weather may also indirectly contribute to the spread of the virus. The best prevention is to cover sneezes and coughs, wash hands thoroughly, and exercise regularly. In the meantime, perhaps it wouldn’t hurt to keep warm anyway.

References

[1] Zuger, A. “You’ll Catch Your Death!” An Old Wives’ Tale? Well… (2003). The New York Times. Retrieved from http://www.nytimes.com/2003/03/04/science/you-ll-catch-your-death-an-old-wives-tale-well.html?pagewanted=1&_r=1
[2] Melone, L. (Medically reviewed by Bass III, P. F. M.D.) Can the Cold Give You a Cold? (2012) Retrieved from http://www.everydayhealth.com/cold-and-flu/colds-and-the-weather.aspx
[3] Gensel, L. The Medical World of Benjamin Franklin (1998). The Journal of the Royal Society of Medicine. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1299336/
[4] Atzl, I., Helms, R. A short history of the common cold (2009). Birkhäuser Advances in Infectious Diseases. Pp 1-21. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1299336/
[5] Tyrrell, D. A. J., Fielder, M. Cold Wars: The Fight Against the Common Cold (1987). The Oxford University Press. Pp 17.
[6] Gwaltney, J. M. Jr., Jordan, W. S. Jr., Rhinoviruses and Respiratory Disease (1964). Bacteriological Reviews. Vol. 28. No. 4, p. 409-422. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC441239/pdf/bactrev00143-0053.pdf
[7] Douglas, R. G. Jr., Lindgren, K. M., Couch, R. B. Exposure to Cold Environment and Rhinovirus Common Cold – Failure to Demonstrate Effect (1968). The New England Journal of Medicine. DOI: 10.1056/NEJM. Retrieved from http://www.nejm.org/doi/full/10.1056/NEJM196810032791404
[8] Eccles, R. Acute cooling of the body surface and the common cold. (2002). PubMed Rhinology. Vol. 40 (3): 109 -14. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/12357708