Mythbusters: The Common Cold: A Misnamed Virus

Alicia Darnell | alicia.darnell@yale.edu October 25, 2009

Mythbusters: The Common Cold: A Misnamed Virus

Winter is guilty of causing quite a bit of discomfort in our lives. It is guilty of reducing us to shivering lumps under piles of blankets, guilty of stubbed toes in dawn darkness, and guilty of chapped lips and dry skin.

Despite popular belief, it is not, however, guilty of causing you to cough and sneeze all night, causing your throat to hurt, or causing your sinuses to weigh ten pounds. Correlation does not always imply causation, and cold weather does not cause the common cold. In fact, freezing in cold weather does not even affect the duration or severity of a cold. You are actually less likely to catch a cold in the act of running around outside in a bathing suit than by huddling inside next to your radiator.

More than 250 viruses are the true culprits behind the miserable sniffling epidemics that spread through Yale in the colder months. Fifty percent of the illnesses we call “colds” are caused by one of about 100 forms of a crafty virus called a rhinovirus. The rest are caused by a family of viruses called coronavi­ruses, or by secondary infections with other respiratory ailments like the flu.

These cold-causing viruses are transmitted in secretions of the upper respiratory system, in aerosol-spray droplet form. In other words, when your diseased suitemates sneeze on you, they are coating you with deadly droplets of saliva and mucus containing viral particles. If any of these droplets come into contact with your eyes or mouth, you are at high risk for infection. However, if that diseased suitemate is considerate enough to direct their sneeze into their hands instead of your eyes, surfaces they touch before washing their hands can still transmit viral particles to your hands – and then if you touch your eyes or mouth, the rhinovirus could then infect you.

Viruses are tiny infectious particles that cannot reproduce without entering a host cell and taking over the genetic machinery of that cell. Viruses inject their viral genetic material into a host cell and cause the cell to become a factor for reproducing the viral genetic material. This eventually causes the cell to lyse (break open) and release a multitude of virus copies that infect new cells.

Rhinoviruses are simple RNA viruses coated by a protein capsid. They enter the body through the upper respiratory tract and bind to inter-cellular adhesion molecule (ICAM) receptors, located on the surface of respiratory tract epithelial cells. When they infect and lyse these cells, the cells release chemical distress signals. The inflammatory effect of these signals causes the symptoms we call the common cold: congestion, sore throat, sneezing, coughing, runny nose, muscle weakness, headache, and fatigue.

Interestingly, we are not all equally suscep­tible to catching colds. Researchers at Carn­egie Mellon University have found a correla­tion between sleep deficiency and decreased immunity to infection by the common cold. As a college student, I can certainly attest to the feeling of total immune system collapse after prolonged sleep deprivation.

So if all of these symptoms are actually caused by airborne or lingering viruses and staying out a little later than we should, why do we blame winter for the common cold? As it turns out, winter plays an indirect role in spreading colds. Cold weather sequesters everyone inside where they infect each other in a concentrated area and coat warm indoor surfaces with viral nuclei, which can live better on warm than on cold outdoor sur­faces. Winter traps us inside so rhinoviruses can get to us more easily. Still, being cold does not cause colds.

What are the implications of busting this myth? You should still bundle up when you go outside, but if you do not want to get a cold, you need to avoid infectious indoor perils. Wash your hands frequently and try to keep your potentially contaminated hands away from your eyes and mouth. I am not advocating hermitage during the winter months – and those surgical masks look a bit silly – but you should keep a safe distance between yourself and watery-eyed, runny-nosed, violently coughing people. If you do happen to catch a cold anyway, as data indicates you will two to four times a year, you will know not to blame it on the weather outside.