Acute viral nasopharyngitis, often known as the common cold, is a viral infectious disease of the upper respiratory system (nose and throat).[1] Symptoms include sneezing, sniffling, runny nose, nasal congestion, scratchy, sore, or phlegmy throat, coughing, headache, and tiredness. In severe and rare cases, symptoms of conjunctivitis (red, itchy, or watery eyes) may also accompany a cold. Those affected may also feel achy. Colds typically last five to seven days, with residual coughing and/or catarrh lasting up to one to two weeks.[2] The common cold is the most common of all human diseases infecting adults at an average rate of 2–4 infections per year, and school-aged children as many as 12 times per year. Children and their parents or caretakers are at a higher risk, possibly due to the high population density of schools and because transmission to family members is highly efficient.

The common cold belongs to the upper respiratory tract infections. It is different from influenza, a more severe viral infection of the respiratory tract that shows the additional symptoms of rapidly rising fever, chills, and body and muscle aches. While the common cold itself is rarely life-threatening, its complications, such as pneumonia, can be.

Most common colds are caused by infection by rhinovirus. Other viruses causing colds are coronavirus, human parainfluenza viruses, human respiratory syncytial virus, adenoviruses, enteroviruses, or metapneumovirus.[2][3]

A cold virus can infect the next person before it is defeated by the body's immune system. Sneezes expel a significantly larger concentration of virus "cloud" than coughing. The "cloud" is partly invisible and falls at a rate slow enough to last for hours—with part of the droplet nuclei evaporating and leaving much smaller and invisible "droplet nuclei" in the air. Droplets from turbulent sneezing or coughing or hand contact also can last for hours on surfaces, although less virus can be recovered from porous surfaces such as wood or paper towel than non-porous surfaces such as a metal bar. The incubation period (time between becoming infected and developing symptoms) is one to three days.[4] The infectious period (time during which an infected person can infect others) begins about one day before symptoms begin, and continues for the first five days of the illness.[4] Symptoms, however, are not necessary for viral shedding or transmission, as a percentage of asymptomatic subjects exhibit viruses in nasal swabs, likely controlling the virus at concentrations too low for them to have symptoms.

The virus enters the cells of the lining of the nasopharynx (the area between the nose and throat), and rapidly multiplies. The major entry point is normally the nose, but can also be the eyes (in this case drainage into the nasopharynx would occur through the Nasolacrimal duct).