The common cold is an illness often related to winter and characterized by nasal congestion and sneezing, sometimes with sore throat, coughing, headache and other uncomfortable respiratory symptoms. The symptoms are the result of an infection in the respiratory tract, which can be due to any one of hundreds of viruses.
Causes of the common cold
A number of viruses can cause the acute respiratory infection that produces a cold, but the most common is rhinovirus. There are more than a hundred types of rhinovirus alone, and they cause up to half of all colds (depending on which health authority you ask). Other viruses infect the same area of the body and cause the same symptoms – respiratory syncytial virus (RSV) is common in children, and coronavirus, adenovirus, and parainfluenza are also associated with cold-like symptoms. These viruses have some things in common, including the fact that they infect the respiratory tract.
Causes of cold-like symptoms
When a virus infects the cells of the respiratory tract it produces an immune response, resulting in inflammation of the infected tissue. Because the various cold viruses infect a similar part of the body, they result in a similar inflammatory pattern. The inflamed cells then produce chemicals (such as histamine) that alter vascular permeability and induce a runny nose and congestion in efforts to thwart other invaders in the sinuses and nasal cavity. The inflammation can also result in soreness of the infected respiratory tract (i.e. the throat or nasal cavity/sinuses), irritation of the area (i.e. sneezing and coughing), and general fatigue due to nonspecific immune responses throughout the body.
Some research has shown that it goes even beyond the normal immune response, though – rhinovirus has been shown to hijack the cell’s genetic mechanisms, over-stimulating the immune response. Other cold viruses may also be associated with more severe infections of the lower respiratory system and other complications. Colds usually are not discerned by the type of viral infection unless other symptoms are present.
What makes a cold “common”
Tens of millions of people suffer from colds each year with similar symptoms, making it one of the most common ailments and medical complaints. Even though the cause could be any number of viruses, it’s the same disorder – coughing, sneezing, congestion, achy, just not feeling well for days or weeks. Because colds are caused by viruses, the condition is self-limiting and simply has to take its course, so a number of home remedies and over the counter solutions to the symptoms have become part of the winter repertoire, including chicken soup, cough syrup, and boxes of tissues on the bedside stand.
The science of colds in winter
The viruses that cause the common cold are spread by human-to-human contact. The time of year when everyone is stuck indoors with each other (i.e. winter or cold weather) provides ample territory for transmission. Colds happen other times of the year, too, they just tend to become more rampant when humans are in closer quarters.