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How Long Is Mono Contagious?

The way mono works in the body is tricky, so lots of people are confused about how long it is contagious. If you get mono, the virus stays in your body for life. That doesn't mean that you're always contagious . But the virus can surface from time to time and risk infecting someone else

Here's how it works:

Mono is short for mononucleosis. It's usually caused by an infection with the Epstein-Barr virus (EBV).

People who have mono can be contagious from the time they first become infected. But they may not know that they have the virus. It takes a while for mono symptoms (like tiredness, fever, muscle aches, headache, or sore throat) to show up — about 4 to 7 weeks, in fact. This is called the incubation period.

To make things even more confusing, some people can carry the virus without ever getting any mono symptoms. Even if they don't know they have the infection, they can still pass it to others.

Mono needs to run its course naturally. Symptoms may last 2 to 4 weeks, and some people feel tired for several weeks longer. That's why it's important to take care of yourself and get lots of rest.

Health experts aren't sure how long people with mono stay contagious after symptoms are gone. They believe that people can spread the infection for many months after that — some studies show as long as 18 months. Then, the virus stays dormant (inactive) in the body for the rest of a person's life.

Sometimes the dormant virus can "wake up" and find its way into a person's saliva (spit). That person might not feel ill or show any mono symptoms, but can spread the virus to other people. So there's a very small chance that people who have had mono in the past can pass it to others, even when they feel OK.

The bottom line is that it's hard to prevent mono from spreading. Because EBV is so sneaky, infections are common. About 95% of people are infected with the virus by the time they are adults. Viruses like EBV are one reason why doctors urge everyone to wash their hands well and often. It's the best way to keep germs at bay.

Reviewed by: Elana Pearl Ben-Joseph, MD
Date Reviewed: 09-05-2018