Kiss of Death...(Or Diseases)

Diseases Spread by Kissing

Couple Wearing Fedoras Kissing
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Love is in the air
Germs are everywhere
Kissers beware
Of infections you can share.

We know that kisses of passion can lead to one thing or another. But did you know that kissing can also lead to an infectious disease? Mononucleosis, or mono, is the prototypical “kissing disease,” and sexually-transmitted diseases are infamous following some romantic interludes. But did you know that there are many infections that can be spread through mere kissing alone?

Infectious Diseases in Saliva

Infectious diseases are spread through several routes of transmission. “Oral transmission” refers to spreading of microbes through saliva, foods or drinks. When a person accidentally consumes microbe-contaminated items, such as saliva during kissing, the swallowing action of the tongue wipes the microbes against the back of the throat, allowing the microbe to enter the body. Infections, such as mononucleosis (the kissing disease), caused by Epstein-Barr virus (EBV), and cytomegalovirus (CMV) are spread via oral transmission from virus-containing saliva.

Other infectious microbes that spread through saliva do so by sticking to the inner surface of the cheeks and mouth, the tongue, or teeth. An example is the bacterium Streptococcus, which can cause an array of infections, including gum disease and strep throat.

An important thing to keep in mind is that the surfaces of the respiratory tract (nose, mouth, and throat) are continuous and made up of similar tissues.

As a result, microbes that are found in the saliva can generally be found in other parts of the respiratory tract, including the nose and throat. Therefore, even colds and flus (and other respiratory infections) can potentially be spread through the saliva.

Infectious Diseases from Mouth Sores

Cold sores
Cold sores are caused by Herpes, usually Herpes Simplex Virus-1 (HSV-1) which is different from Herpes Simplex Virus-2 (HSV-2) which is more generally associated with genital herpes.

In contrast to infections spread through the saliva, HSV-1 is spread through open cold sores on the lips or near the mouth. Although the infection is contagious through all stages of a cold sore, the infection is most contagious when the sore is open and leaking fluid.

Hand, foot, and mouth disease
Hand, foot, and mouth disease, caused by Coxsackie virus, is another infectious disease that is spread through open sores in the mouth. This is a type of enterovirus, which is a common infection that has multiple strains that we all often are exposed to. This particular infection is common in kids, especially those in daycare or preschool settings. It spreads primarily via the fecal-oral route, a common problem among daycares, since changing of diapers goes on all day.

But canker sores are not infectious.
In contrast to cold sores and coxsackie virus blisters, canker sores have no infectious disease origin and cannot be spread through the saliva or kissing.

What about HIV and Hepatitis B Virus?

HIV and hepatitis B Virus (HBV) are blood-borne and sexually-transmitted infections that have been found in the saliva. Kissing is, in general, not considered a risk factor for HIV transmission. (It would only be if bleeding occurred or open sores were present).

In contrast, transmission of hepatitis B virus through saliva has been documented, though the infection is usually transmitted through sexual contact or blood. Meanwhile, other types of hepatitis are not related to kissing. Hepatitis A requires some form of fecal exposure (which would include contaminated water or anilingus) and Hepatitis C requires blood exposure. It's therefore possible that Hep A or C could be transmitted through kissing if there are open sores or remnant fecal matter in the mouth, but extraordinarily unlikely.

Natural Microbial Defense Mechanisms in the Mouth

Saliva has a natural cleansing role, provided by its flushing activity.

Other antimicrobial defenses in the saliva include antibodies and other antimicrobial proteins (e.g., lysozyme), and normal mouth flora (the “good” bacteria that prevents growth of “bad” bacteria). We also have all sorts of viruses naturally in our bodies at times, including in our mouths.

The spread of infectious microbes through the saliva can occur when natural resistance in the mouth is reduced. For example, gum infections can occur in people with vitamin C deficiencies, and thrush, caused by Candida yeast infections, is more likely to occur in people who have been taking antibiotics. People who are dehydrated have reduced salivary flow and four times more bacteria in their mouths.

Preventing Kissing Diseases

Be careful who you kiss.


Mims CA, Playfair JH, Roitt, IM, Wakelin D, Williams R, and Anderson RM. Medical Microbiology. ©1993. Mosby-Year Book Europe Limited. London, UK.

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