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Last Updated August 2022 | This article was created by editorial staff and reviewed by Peter Rippey, MD, CAQSM

What is mononucleosis?

Mononucleosis (often called “mono”) is a contagious illness. It’s usually caused by the Epstein-Barr virus, but can be caused by other viruses, too. It’s spread through saliva. For this reason, it’s sometimes called the kissing disease. It’s most common in teens and young adults. However, anyone at any age can get it.

Symptoms of mono

Some of the symptoms of mono are similar to those of a cold or flu. Symptoms often don’t appear until 4 to 6 weeks after you’ve been exposed to the virus. Symptoms may not come at the same time, and they may come on gradually. They include:

  • Fatigue
  • Fever
  • Sore throat
  • Weakness
  • Swollen glands in your neck and armpits
  • Swollen spleen or liver
  • Loss of appetite
  • Rash

Symptoms in young children are generally mild. Symptoms in adolescents and young adults tend to be more severe.

What causes mono?

Most cases of mono are caused by the Epstein-Barr virus. The virus is found in saliva, mucus, and other body fluids. It can be passed between people many ways. It can be passed through exposure to a cough or sneeze. It can be passed by sharing food utensils (such as drinking glasses, spoons, and forks). It even can be passed from one person to another through kissing.

How is mono diagnosed?

Your doctor will probably first ask you some questions about your symptoms. He or she will do a physical exam and look for:

  • Swollen lymph nodes in your neck
  • Swollen tonsils
  • Swollen liver or spleen

Your doctor will probably order blood tests to confirm the diagnosis. One common test used to diagnose mono is called the Monospot test. Sometimes other blood tests are needed if the results of the Monospot test aren’t clear.

Can mono be prevented or avoided?

There is no vaccine to prevent mono. The best thing you can do to avoid it is to stay away from anyone you know who has it. Don’t kiss or share utensils or other personal items with someone who is sick (or has symptoms).

Mono treatment

There isn’t a cure for mono. The virus will go away on its own. Symptoms usually last about 4 weeks. The main goal of treatment is to relieve your symptoms. Here are some steps you can take to feel better:

  • Rest. Sleep helps your body fight infection.
  • Drink plenty of fluids. They help prevent dehydration.
  • Soothe a sore throat. Gargle with saltwater or suck on throat lozenges, hard candy, or flavored frozen desserts (such as Popsicles).
  • Relieve the pain. Take acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) to relieve pain and fever. Do not give aspirin to children. Aspirin has been associated with a rare disease in children called Reye’s syndrome. Reye’s syndrome is a serious illness that can lead to death.

Do I need an antibiotic?

Antibiotics are not effective against mono. Mono is caused by a virus. Antibiotics don’t work against viruses. If you have a bacterial infection (such as strep throat) in addition to mono, your doctor may give you an antibiotic to treat that infection. Taking antibiotics for mono may cause an itchy rash.

What about sports and exercise?

Avoid sports, physical activities, or exercise until your doctor tells you they’re safe. Moving around too much puts you at risk of rupturing (bursting) your spleen, especially if it’s enlarged. A ruptured spleen, while uncommon, causes bleeding that can be fatal. You’ll need to avoid physical activities and contact sports for about 3 to 4 weeks after you’ve had mono—or until your doctor tells you it is safe.

Living with mono

Most people feel better in 2 to 4 weeks. Fatigue may last for several more weeks. In some cases, symptoms can last for 6 months or longer. In addition, mono can sometimes have complications. The main complication is the enlargement of the spleen. The spleen is like a large gland. It’s located in the upper part of your abdomen on the left side. It helps filter your blood. In severe cases of mono, the spleen can rupture (tear open).

A ruptured spleen is rare in people who have mono. But it’s wise to be aware of the signs:

  • Sharp pain in the left upper part of your abdomen (under the left chest)
  • Feeling lightheaded
  • Feeling confused
  • Blurred vision
  • Fainting

Other complications can include anemia, nervous system problems, or hepatitis with jaundice. These could cause symptoms including:

  • Breathing difficulty
  • Persistent high fevers (101.5 degrees or higher)
  • Severe headache
  • Weakness in arms or legs
  • Yellow color in your eyes or skin (jaundice)
  • Trouble swallowing

Call your doctor right away if you notice any of the above symptoms.

Questions to ask your doctor

  • How did I get mononucleosis?
  • I have mononucleosis. Should my girlfriend or boyfriend get tested?
  • What’s the best treatment for me?
  • How long will it be before I can exercise safely?
  • How can I make sure that the rest of my family doesn’t get mono?
  • Are there any medicines I can take to feel better?
  • How long will I be contagious?
  • If I start having pain in my side, should I call my doctor immediately?
  • If I have mono once, will I get it again?
  • How long should I keep my child home from school?
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