A cold - also called infectious rhinitis - is a viral infection of the nose and throat. Doctors call it a "self-limiting" condition, which means that it only lasts so long and goes away on its own.
Colds are relatively harmless, but they have important social and economic impact. It is estimated that 40% of time lost from work and 30% of school absences are due to the common cold. Cold symptoms normally improve within 1 week, although some may last as long as 2 weeks.
There are over 200 different viruses responsible for causing colds. The most common type are the rhinoviruses, which cause about 40% of colds in adults. Colds occur most often from fall to early spring, when people tend to stay indoors - facilitating easy spread of these viruses.
Common colds are infectious, and can be passed from one person to another. The average adult gets about 2 to 4 colds per year, most often during the winter. Infants can get as many as 8 to 10 colds in a year because their body's defences aren't yet developed. Children under 6 years of age average about 6 to 8 cold episodes each year.
Sneezing or coughing can easily transmit cold virus in droplets from an infected person's mouth or nose. Hand-to-hand contact is another way the virus is passed around. Since cold viruses can live for several hours on hard surfaces, you can even get infected by picking up an object, turning a door handle, or answering a phone recently touched by a person with a cold. It then takes hold by being rubbed into the eyes, nose, or mouth.
Cold viruses invade the tissues that line the inside of the mouth, throat, and nose. This infected membrane becomes swollen or inflamed, and cold symptoms begin.
It usually takes anywhere from 1 to 3 days for symptoms to develop. The cold runs its course in about 7 to 10 days. Symptoms follow a typical pattern:
Colds may aggravate the symptoms of other conditions, such as asthma and chronic obstructive pulmonary (lung) disease (COPD). Colds can also lead to acute bacterial bronchitis, strep throat, pneumonia, or ear infections, especially for people with lung disease.
It's not clear if fatigue, stress, or poor diet and poor health lead to more frequent colds, but they do appear to trigger more severe cold symptoms. Seniors especially tend to get more severe cold virus infections.
The cold virus can also infect other parts of the body. For instance, the eye infection known as pinkeye (mild conjunctivitis) can occur. Kids are especially prone to this, since they tend to wipe their noses with their hands and then rub their eyes.