Mumps is caused by a paramyxovirus that is found in saliva. When an infected person sneezes or coughs, droplets spray into the air and mucus can land in other people’s noses and throats when they breathe. The virus can also be spread by sharing utensils or drinking glasses with an infected person.

The incubation period (the time that elapses between exposure to the virus and the development of symptoms) for mumps is between 14 and 25 days. A patient with mumps is contagious two to three days before the parotid glands (glands that produce saliva in the mouth) begin to swell and until the swelling subsides (usually about nine days later).

Mumps is rare in the United States because most people receive vaccinations at a young age. However, exposure to an infected person may result in mumps in those who have not received vaccinations or have received only a partial vaccination and have not developed sufficient immunity to the disease. Mumps is more common in other countries because the vaccine is not as widely available.

People who have had mumps develop a resistance against it and, therefore, will probably not get it again. People who were born or lived in the United States before 1957 are also likely to be immune from mumps because they probably lived through an epidemic and were exposed to it. After exposure, the immune system develops resistance, even if symptoms are not experienced.