How Long Is Mono Contagious?

The kissing disease has a tricky period of infectiousness

Man and woman kissing.
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Mononucleosis, also known as "mono," is caused by the Epstein-Barr virus (EBV). It is mainly spread through saliva which is why it is commonly referred to as the "kissing disease."

Symptoms of mono can vary from person to person but usually involve extreme fatigue, enlarged tonsils, and sore throat. Depending on the severity of symptoms, the doctor may recommend bed rest, in part to avoid further spread of the virus.

While some people with mono will feel better within a week or two, there are others who may experience symptoms for as long as six months. In rare cases, fatigue may persist for even longer.

Period of Contagiousness

Researchers aren't entirely sure how long a person with acute mono will remain contagious. While many will give you the "all clear" sign after six months, a number of studies have shown that there may be a potential for infection for as long as 18 months. This is because the EBV virus may still be active even if you have no symptoms.

After the initial infection has fully resolved, the virus will go into dormancy and remain in a non-infective state. It will not disappear from the body but will also not be contagious.

And, that's the important thing to remember: once you have been infected with EBV, you will always have EBV. In fact, around 95 percent of people in the U.S. will eventually get the virus, usually before the age of 40.

In some cases, it may be passed from mother to child without any major incidence or complications. More often than not, the infection will occur during the teen years.

While EBV will remain relatively dormant after the initial infection, there may be periods when the virus may suddenly "wake up" and have the potential to infect.

In such case, the person with EBV may feel tired or have swollen glands but be otherwise unaware that he or she is contagious. At other times, there will be no symptoms.

Preventing Mono

What is important to understand is that the resolution of mono symptoms does not mean that a person is any less contagious. Because of this, you need to take precautions to avoid the further spread of infection, including:

  • Avoiding kissing
  • Avoiding shared utensils
  • Avoiding shared drinks or drinking straws

EBV may also be present in vaginal fluids and semen. While oral sex is not considered the predominant mode of transmission, research suggests that higher rates of mono are seen in sexually active teens. As such, sexual activity may need to be curbed during the active stages of infection as an added precaution.

In the end, it is pretty difficult to prevent mono from spreading, which is why you need to take the appropriate care if you or others you know have been infected.


Centers for Disease Control and Prevention. "Epstein-Barr Virus and Infectious Mononucleosis." Atlanta, Georgia; updated September 14, 2016.

Eligio, P.; Delia, R.; and Valeria, G. "EBV Chronic Infections." Mediterr J Hematol Infect Dis. 2010; 2(1): e2010022. DOI: 10.4084/MJHID.2010.022.

Thompson, A. "Infectious Mononucleosis." JAMA. 2015; 313(11):1180. DOI: 10.1001/jama.2015.1592017.