Colds are caused by a viral infection of the upper respiratory tract. On average, adults will get colds approximately four times each year, but children may get colds up to 10 times yearly, according to the Mayo Clinic.
The common cold can be caused by as many as 200 different kinds of viruses. However, the rhinovirus is the most common cause of colds. All cold viruses are highly contagious.
The symptoms of a cold include runny nose, sneezing, itchy/watery eyes, coughing and upper respiratory congestion. Colds viruses differ from other viruses in that they rarely cause fever.
Cold viruses grow and multiply in the nose, reaching their highest concentration three days after infection. Colds can be spread through contact with the nasal discharge of an infected person. This is often occurs when an infected person coughs or sneezes.
Cold viruses may also be spread when a person who has a cold touches an object after blowing her nose or coughing and sneezing into her hand. A person can become infected when she touches a surface that has been contaminated by cold germs in this manner.
Colds rarely cause serious complications; however, in some instances colds can result in ear infection or sinusitis (inflammation of the nasal cavities).
The immune system in healthy persons normally suppresses the cold virus on its own and all symptoms disappear within one week. Over-the-counter pain relievers, decongestants and cough medication may be taken to help cold sufferers cope with symptoms.