Mono, or mononucleosis, is spread through direct contact with saliva. This includes sharing eating utensils, drinks, and even things like lip gloss, lipstick, or lip balm.
Because it takes about 4 to 7 weeks for symptoms to appear, a person who’s infected can spread the virus without even knowing it. Though no one really knows exactly how long it takes after infection with the virus for someone to become contagious, it’s pretty safe to say that a person is most contagious from right before symptoms start until they go away.
If you have shared drinks with, or kissed someone who has mono, there is no way to tell whether you will get it — unless you know you have had mono before. People who have already been infected with the virus that causes mono — Epstein-Barr virus or EBV — probably won’t get reinfected because they develop immunity. (Although it is possible for the virus to “reactivate,” it is not because someone infects you all over again. It is because in rare cases the original virus can flare up and cause symptoms a second time).
About 95% of adults have been infected with EBV, and 50% of kids are infected before age 5. So you may very well have already had mono and not known it.
If you do get the symptoms of mono — such as fever, sore throat, and tiredness — you should see a doctor to find out whether you need an appointment. If so, you will be examined, and may also do a blood test for mono. Other viruses and some bacterial infections — such as strep — may cause similar symptoms.
It is also possible to get mono even from just a quick peck on the lips. That is because the virus is carried in saliva. So it can be spread through any contact with saliva — even from sharing forks, spoons, drinking straws, cups, or lip balm and lipstick.
If you kissed or shared a drink with someone who has mono, it doesn’t mean you will definitely get mono yourself. But because the virus is so contagious, it’s a good idea to avoid kissing or sharing utensils or cosmetics with a person who is sick or may have mono or who recently had it. (Mono can also be spread before people even know that they have it.)