Last reviewed and revised February 27, 2013
"You'd better be careful whom you kiss," I was told. I was in high school and infectious mononucleosis (also called mono) was "going around." Kids missed school for a month; and everyone was told it was because "too many people were kissing too many people."
As it turns out, there were only two or three kids who had mono, and they didn't even know each other. The rest of it was hysteria, rumor or myth. But I always wondered about "kissing disease," as many called it. Was it really dangerous? Was kissing really so risky?
Infectious Mononucleosis: A Viral Infection
Mono is caused by infection with Epstein-Barr Virus (EBV). After exposure to EBV, there are usually no symptoms at all — in fact, up to 95% of adults have antibody evidence of past EBV infection even though the vast majority recalled no related illness; for many, this occurs during early childhood. For reasons that remain unknown, only some people develop mono after exposure to EBV, with fatigue, headache, muscle or joint aches, fever, enlarged lymph nodes and sore throat.
While it is true that the virus is shed in the saliva and can be transmitted by kissing, mono is not the most contagious illness — the common cold is more contagious — and it can be transmitted by other means, such as coughing or sneezing. Preventing the spread of EBV is not easy since there are often no symptoms. Even when there are, one may be contagious before the illness is recognized.
Other infections can cause illness resembling mono, including cytomegalovirus (CMV) and other viral infections. Blood tests usually can establish the diagnosis of mono when necessary.
There is no effective therapy for mono, although acetaminophen or ibuprofen and fluids can be helpful in relieving symptoms. The vast majority of people who have it recover completely within a week or two. Occasionally fatigue lasts more than month, but even then, a return to normal is expected. Because the spleen may become enlarged and could rupture if injured, people with mono are advised to avoid contact sports for at least a month after recovery.
Infections Related to Kissing
During any exchange of bodily fluids, there is a risk of transmitting infectious agents. However, the body has defense systems in place to prevent infection. These work better for some infections than others. For example, HIV and hepatitis B are relatively easy to transmit through sexual intercourse, while hepatitis C is not as readily spread sexually.
Similarly, some infections are harder to transmit through kissing than others. HIV is rarely (if ever) transmitted through kissing; when it does occur it probably relates to open sores in the mouth that allow exposure to blood, not just saliva. On the other hand, many other viral infections are easy to transmit by kissing: herpes simplex virus (HSV, type I), the cause of cold sores or fever blisters, is a common example. In fact, the illnesses commonly transmitted by kissing, including mono, usually have a minimal impact on overall health.
The Bottom Line
While it is true that EBV is easy to transmit from one person to another through kissing, there is usually no recognized illness associated with the infection. Even when mono does follow, complete recovery in a short period is the rule. While "kissing disease" is real, kissing is rarely a danger to your health.
Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.