What is mononucleosis?

Mononucleosis, also known as "mono," is an infectious disease that is usually caused by the Epstein-Barr virus (a herpes virus). Other viruses can also cause mononucleosis. Mononucleosis is not considered a serious illness, but its symptoms may be severe enough to prevent a person from engaging in normal activities for several weeks. The classic symptoms of this illness tend to occur more frequently among teenagers, especially those 15 to 17 years old, and in adults in their 20s.

How common is mononucleosis?

The Epstein-Barr virus is a very common virus. About 85% to 90% of American adults have developed antibodies to the Epstein-Barr virus by the time they are 40 years old, which means that they have been infected with the virus at some point in their lives. Most individuals are infected with this virus early in life (before the adolescent years), and most of these children have no or very mild symptoms from it. Adolescents, especially teens 15 to 17 years of age, and young adults who become infected with this virus are most likely to develop the classic symptoms of mononucleosis.

How is mononucleosis spread?

Mononucleosis is usually acquired by contact with the saliva or mucus of a person who is infected with or is carrying the virus. (Mononucleosis is also known as the "kissing disease," because it can be acquired through kissing.) Occasionally, it can be spread by coughing or sneezing, or when an infected person shares food or tableware with another person.

What are the symptoms of mononucleosis?

The most common symptoms of mononucleosis are fever, sore throat, and swollen lymph glands in the neck, under the arms, and in the groin area. Other symptoms include the following:

In addition to these symptoms, the spleen (an abdominal organ that stores and filters blood) may become enlarged. About half of those who have mononucleosis have enlargement of the spleen sometime during the course of their illness.

The incubation period—the time it takes symptoms to appear after a person becomes infected with the virus—can be 4 to 6 weeks. Symptoms of mononucleosis usually last for 1 to 4 weeks, but it might take as long as 2 months before you feel well enough to resume all of your normal activities.

Are there any symptoms of mononucleosis that require medical attention?

If you have an unusually painful or persistent sore throat or have difficulty breathing or swallowing because your tonsils are swollen, see a healthcare professional. Your doctor may perform a throat culture to see if you have a streptococcus infection (strep throat), which is not uncommon when you have mononucleosis, and which can be treated with antibiotics. You can also develop airway difficulties from enlarged tonsils.

If you have mononucleosis and feel a sudden, sharp, severe pain in your left side in the upper abdomen, go to a hospital or call 9-1-1. The pain may be a sign of a ruptured spleen, which is a very rare complication of mononucleosis.

Symptoms lasting longer than 4-6 weeks are very rarely due to the effects of mononucleosis.

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