common cold

An ancient belief still common today claims that a cold can be "caught" by prolonged exposure to cold weather such as rain or winter conditions, which is where the disease got its name. Although common colds are seasonal, with more occurring during winter, experiments so far have failed to produce evidence that short-term exposure to cold weather or direct chilling increases susceptibility to infection, implying that the seasonal variation is instead due to a change in behaviors such as increased time spent indoors at close proximity to others. With respect to the causation of cold-like symptoms, researchers at the Common Cold Centre at Cardiff University conducted a study to "test the hypothesis that acute cooling of the feet causes the onset of common cold symptoms." The study measured the subjects' self-reported cold symptoms, and belief they had a cold, but not whether an actual respiratory infection developed. It found that a significantly greater number of those subjects chilled developed cold symptoms 4 or 5 days after the chilling. It concludes that the onset of common cold symptoms can be caused by acute chilling of the feet. Some possible explanations were suggested for the symptoms, such as placebo, or constriction of blood vessels of the nasal passages which might lead to reduced immunity, however "further studies are needed to determine the relationship of symptom generation to any respiratory infection." Another possibility which remains to be explored involves the role that proteins of the complement system play in the prevention of a sustained infection. Decreased temperature may result in a drop in tissue permeability and, as a result, may lead to reduced plasma leakage. Among the many proteins suspended in plasma are complement proteins which serve to disable, destroy, or tag for destruction foreign particulate (in this case viral capsids). Thus, sustained exposure to cold may inhibit the effectiveness of the complement system and allow the virus a better chance of establishing a state of infection. ICAM-1, the receptor that Rhinovirus binds to in order to infect cells, is known to increase in number and receptiveness in response to many irritants, including dust and pollen. That a cold climate in combination with varying degrees of humidity can act as a similar "irritant" needs to be investigated.