The common cold or upper respiratory infection (URI) is a common infectious disease of the nose and throat, the upper respiratory system. Its symptoms are sneezing, sniffing, scratchy throat, coughing and headache; they typically last for 4-10 days.
The disease is caused by several viruses (mainly rhinoviruses, coronaviruses and also certain echoviruses and coxsackieviruses). These are transmitted from person to person by droplets resulting from coughs or sneezes. The droplets are either inhaled directly, or, more commonly, transmitted from hand to hand via handshakes or door knobs, and then ingested when the hand touches the face.
The term "cold" is misleading, as the temperature does not play a role, nor are any other factors known which increase or decrease the probability of infection. Colds are somewhat more common in winter since during that time of the year people spend more time indoors in close proximity of others, increasing the infection risk. Some factors influence the severity of symptoms, for instance psychological stress and position in the menstrual cycle.
The virus enters the cells of the lining of the nose and throat, and multiplies inside them. The symptoms are a result of the body's defense mechanisms: sneezes, runny nose and coughs to expel the invader, and inflammation to attract and activate immune cells. The virus takes advantage of sneezes and coughs to infect the next person just in time before it is killed by the immune system.
Treatment for the common cold is designed to relieve the symptoms rather than attack the cause. Common treatments include analgesics such as paracetamol (acetaminophen) as well as localised versions targeting the throat (often delivered in lozenge form), nasal decongestants (which work to reduce the inflammation in the nasal passages) and cough suppressants (which work like a narcotic to suppress the cough reflex of the brain). A warm and humid environment and drinking lots of fluids, especially hot liquids, alleviate symptoms somewhat. For most people, even without these remedies, colds are relatively minor inconveniences and they can go on with their daily activities with a little discomfort.
To prevent infection, frequent hand washing is helpful, especially if infected people are around. In some countries, people with the common cold wear surgical masks out of courtesy. Because of the large variety of viruses causing the common cold, vaccination is impractical.