Not everyone infected with the virus that causes mono (Epstein-Barr virus, or EBV) has symptoms. This is especially true in young children, who may have a fever but no other symptoms. People between the ages of 10 and 24 are most likely to have obvious symptoms.^{1, 2}

The most common symptoms of mono are:

• Fever, which may range from 101 F to 104 F, and chills.
• Sore throat, often with white patches on the tonsils (which may look like strep throat).
• Swollen lymph nodes all over the body, especially the lymph nodes in the neck.
• Swollen tonsils.
• Headache or body aches.
• A lack of energy and fatigue.
• Loss of appetite.
• Pain in the upper left part of the abdomen, which may indicate that the spleen has become enlarged.

These symptoms usually get better within one or two months.

Mono can cause a rash if you take antibiotics such as penicillin, ampicillin, or amoxicillin. These antibiotics are often prescribed for other causes of sore throat, such as strep throat, and might be prescribed for you before the doctor knows you have mono. The rash is not an allergic reaction.³

Mono may cause your spleen to swell to 2 or 3 times its normal size. An enlarged spleen occurs in up to half of those with mono.⁴ A blow to the abdomen can cause an enlarged spleen to rupture. To reduce this risk, avoid heavy lifting and contact sports for 3 to 4 weeks after you become ill with mono or until your doctor says it is safe. In very rare cases, the spleen may rupture on its own.

Symptoms of mono can be more severe and last longer in people who have an impaired immune system or a rare genetic condition called X-linked lymphoproliferative syndrome.

The symptoms of infectious mononucleosis, such as a sore throat and fever, are found in many other conditions as well.