How Long Is Mono Contagious?

The kissing disease has a tricky period of being contagious

Man and woman kissing.
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Mononucleosis (mono), also known as "the kissing disease," is caused by the Epstein-Barr virus (EBV). It is mainly spread through saliva. While infants are breastfeeding, they are protected from an EBV infection. After children are no longer receiving antibodies through their mother's breast milk, exposure to EBV can cause a mild illness that may be similar to many other childhood illnesses. Once your child has matured into adolescence or becomes a young adult, infection with EBV will cause infectious mononucleosis approximately 35 to 50 percent of the time.​

Symptoms of mono range in severity from person to person, but usually include extreme fatigue, enlarged tonsil, and an extremely sore throat. Your doctor will most likely ask that you take a leave of absence from school or work so that you can get adequate rest to help with the recovery, as antibiotics will not help you get over a viral infection.

How Long Is It Contagious?

At this point in time, there is not a confirmed answer as to how long a person with an acute (current) infection of mono remains contagious. What further complicates an adequate answer to this question is that once having mono, EBV will remain in your body for the rest of your life. However, it is important that you know that EBV usually remains in the body in a dormant, sleeping state. While dormant, you cannot pass mono to someone else by kissing them. However, there is the chance that your dormant EBV infection will reactivate.

A reactivated EBV infection may or may not be accompanied by symptoms.

Some research shows that even in the late stages of a mono infection, a high number of EBV remains in the saliva. Some studies have shown that you may still be contagious from infectious mononucleosis for greater than six months.

You should start feeling better within one to two weeks and most people will have a resolution of their symptoms well before six months. In rare cases, persistent fatigue may occur after an acute case of mono.

If you are still seeing fatigue after several months, you will likely be worried. There is a 10 percent risk that you can acquire chronic fatigue syndrome (CFS) from an EBV infection. While not always curable, there are a lot of resources on how to deal with CFS, and your physician can also help manage any lingering effects from a mono infection. If you are experiencing chronic fatigue and have fully recovered from mono, the persistent fatigue does not mean that you are still contagious.

What Should I Avoid Doing While I Am Contagious?

It's hard to prevent the spread of mono because EBV is actually present in the majority of the population. Approximately 95 out of 100 people between the ages of 35 and 40 are carriers of Epstein-Barr virus. However, the majority of those people will not be contagious. While you are having symptoms of mono and until you are fully recovered, there are some basic things that can help you from spreading it to others who have not had a prior exposure to the virus:

  • Avoid kissing.
  • Do not share eating utensils with others.
  • Do not drink from the same glass as others.

There is some research suggesting that sexual intercourse may be a possible risk factor for acquiring EBV, but that is not known for certain. One thing to remember is that despite feeling better, you may be contagious and may not know when your dormant infection may reactivate. It is important to be cautious but realize that, unlike a cold or the flu, you cannot always prevent mono from spreading.


Centers for Disease Control and Prevention. Epstein-Barr Virus and Infectious Mononucleosis.

Fafi-Kremer S, Morand P, Brion JP, Pavese P, Baccard M, Germi R, Genoulaz O, Nicod S, Jolivet M, Ruigrok RW, Stahl JP, Seigneurin JM. 2005. Long-term shedding of infectious epstein barr virus after infectious mononucleosis. The Journal of Infectious Disease 191 (6): 985-989. 

Up-to-date. 2011. Patient information: infectious mononucleosis (mono) in adults and adolescents

White, P.D. (2007). What Causes Prolonged Fatigue after Infectious Mononucleosis—and Does It Tell Us Anything about Chronic Fatigue Syndrome? J Infect Dis. 196 (1): 4-5. doi: 10.1086/518615