There's a good reason why lots of people are confused about
how long mono is contagious. That's because the way mono works
within the body is tricky.
Mono is short for mononucleosis. It is caused by an infection
with the Epstein-Barr virus (EBV), a virus in the herpes family of
Once someone gets mono, the virus stays in that person's
body for life.
But this doesn't mean that if you've had mono you
are always contagious.
Over time, the virus becomes less contagious. Eventually, it's
very unlikely that a person who had mono will transmit the virus to
People who have mono can be contagious from the time they first
become infected with the virus. But they may not know that they
have the virus in its early stages. That's because it takes a
while from the time a person is infected to the time symptoms of
mono show up - about 4 to 7 weeks in fact. (This is called the
To make it even more confusing, some people can carry the virus
without having any symptoms of mono, so they might not know they
have the infection at all.
Mono needs to run its course naturally over about 2 to 4 weeks -
and some people feel tired for several weeks longer. It's
take care of yourself
if you have mono and get lots of rest.
Doctors and researchers aren't exactly sure how long someone
with mono stays contagious after symptoms are gone. But it's
generally believed that a person can spread the infection for many
months after the symptoms are completely gone - some studies show
as long as 18 months. But after that, it's very unlikely that a
person will give someone else mono.
Larissa Hirsch, MD
Date reviewed: November 2006
Originally reviewed by:
Stephen C. Eppes, MD
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
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