young couple kissing
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What Is It?

Mononucleosis, or “mono,” is a viral infection that can cause flu-like symptoms that usually show up 4 to 6 weeks after you get it. It’s sometimes called the “kissing disease” because the virus often spreads through smooches.

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What Causes It?

The most common culprit is the Epstein-Barr virus. But other viruses also can give you  mononucleosis. Just because you get the virus doesn’t mean it will turn into a full-blown case of mono. Many people who are infected, especially small kids, have very few, if any, symptoms.

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You might feel more tired than usual and have a mild fever and sore throat. Your lymph nodes, tissue that normally acts as filters, may swell under your arms and in your neck and groin area. You also may have body aches and pains, swollen tonsils, headache, and even a skin rash.

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Who Gets It?

Anyone can get mono. But teens and people in their early 20s are most likely to have symptoms serious enough to notice. By then, even if you haven’t felt sick, you almost surely already caught the Epstein-Barr virus. If so, you probably won’t get mono again.

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How Do You Get It?

The virus lives in the spit of someone who has mono. So you can catch it from kissing them, or sharing cups, spoons, and other items. Mono doesn’t spread as easily as the common cold, but you could get it through a cough or sneeze if you’re nearby. Other bodily fluids, like blood and semen, may also pass it on.

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When Is It Contagious?

When you’re sick, for sure. But you also can give mono to someone even before you know you have it. That’s because the virus may incubate for 4 to 7 weeks before you notice any signs. Even then, you may not recognize it as mono because your symptoms may not all happen at once. Some studies show you can pass on the virus for as long as 18 months after you recover. 

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Tell your doctor about all your symptoms and if you’ve had mono before. They’ll examine you, possibly checking your lymph nodes, tonsils, spleen, and liver for swelling. This is usually enough to diagnose it, though in some cases you might need a blood test for Epstein-Barr antibodies, unusual white blood cell activity, or changes in the way your liver works.

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Neither antibiotics (which fight bacteria) nor antiviral drugs work against mono. Ibuprofen or acetaminophen can help with headache, fever, and body aches, but there are no medications that can cure or even shorten your bout of illness. Never give aspirin to a child sick from mono or any other virus because it can cause a serious condition called Reye’s syndrome that can damage the liver. 

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What You Can Do

It’s important to rest, especially early on, when you feel the worst. That may help prevent complications and keep you from feeling sicker. Drink lots of water and other liquids to keep your body hydrated. Ice pops and other icy foods can relieve your sore throat, and it can help to gargle with saltwater solution several times a day. With plenty of rest and fluids, most cases aren’t serious and get better within a few weeks.

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There’s no vaccine for mono. If someone you know has it, don’t lock lips with them! To be really safe, wait several days after the person no longer has symptoms, especially fever. Wash your hands regularly, and avoid sharing food, drinks, and personal items like toothbrushes. There’s not much else you can do to stop yourself from getting the virus. That’s why 95% of Americans have it in their system by the time they’re adults.

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No Roughhousing

One possible symptom of mono is an enlarged spleen. This makes it easier to break open, causing pain and bleeding inside your body that could require emergency surgery. So stay away from contact sports like football and vigorous activities like weightlifting, tumbling, or roughhousing with friends. Doctors usually recommend you wait at least a month after symptoms are gone.

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Other Complications

Mono can inflame your liver and cause jaundice that yellows your skin and the whites of your eyes. Less often, it can inflame the heart muscle (myocarditis), cause clotting problems, infect the nervous system (meningitis, Guillain-Barre), and make your red blood cells drop (anemia). Sometimes, tonsils can get so swollen that they make it hard to breathe. Talk to your doctor if you notice any of these signs.

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Sources | Medically Reviewed on 03/04/2019 Reviewed by Carol DerSarkissian on March 04, 2019


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2) James Cavallini / Science Source

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12) Garry Watson / Science Source



CDC: “About Infectious Mononucleosis.”

Mayo Clinic: “Mononucleosis.”

The Cleveland Clinic: “Mononucleosis.”

The Nemours Foundation: “Mononucleosis,” “How Long Is Mono Contagious?”

Reviewed by Carol DerSarkissian on March 04, 2019

This tool does not provide medical advice. See additional information.

THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional medical advice, diagnosis or treatment and should not be relied on to make decisions about your health. Never ignore professional medical advice in seeking treatment because of something you have read on the WebMD Site. If you think you may have a medical emergency, immediately call your doctor or dial 911.