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If you've ever heard of "mono," then you know of at least one "kissing disease." Mononucleosis (mono) is probably one of the most well-known infectious diseases among adolescents. While many people know that they can acquire a sexually transmitted disease from intercourse, there are also many infections that can be spread through mere kissing alone.
Infectious diseases can be spread through several routes of transmission. Oral transmission refers to the spreading of microbes through saliva or shared foods and 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 caused by Epstein-Barr virus (EBV), and cytomegalovirus (CMV), are examples of infections 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.
The surfaces of the respiratory tract (nose, mouth, and throat) are continuous and made up of similar tissues. 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 flu (and other respiratory infections) can be spread through saliva.
Certain infections causing ulcerations in the mouth can also be spread through kissing. These include cold sores and hand, foot, and mouth disease.
Cold sores are caused by the herpes virus, usually herpes simplex virus-1 (HSV-1). While related, this 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, caused by the 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 infection is common in kids, especially in daycare or preschool settings.
It spreads by breathing the air after the sick person coughs or sneezes, touching or close contact such as kissing or sharing utensils and cups, through touching an ill person's feces such as when changing a diaper, or from touching the eyes, nose, or mouth after contact with surfaces that have been contaminated such as doorknobs or toys.
In contrast to cold sores and coxsackievirus blisters, canker sores have no infectious disease origin and cannot be spread through saliva or kissing.
Hepatitis B is spread through contact with body fluids infected with the virus, such as direct contact with blood or open wounds. Therefore, it can be spread through sharing a toothbrush, but not through sharing eating utensils, kissing, coughing, or sneezing.
Hepatitis C requires blood exposure and is typically spread through the use of shared needles or other equipment used to prepare and inject drugs. Hepatitis A requires some form of fecal exposure (which would include contaminated water or food), and is not spread via saliva or kissing.
Kissing is, in general, not considered a risk factor for HIV transmission. It would only be a risk if bleeding occurred or open sores were present.
Saliva has a natural cleansing role, provided by its flushing activity. Other antimicrobial defenses in the saliva include antibodies and other antimicrobial proteins (such as lysozyme).
The normal mouth flora (the “good” bacteria) prevent the growth of “bad” bacteria. You also have all sorts of viruses naturally in your body at times, including in your mouth.
People are more likely to get mouth infections when natural resistance in the mouth is reduced. For example, gum infections can occur in people with vitamin C deficiencies. Thrush, caused by candida (yeast) infections, is more likely to occur in people who have been taking antibiotics.
A social kiss is not considered a risk for HIV since body fluids are not transmitted from one person to another. However, in rare instances, it may be possible to pass HIV on if both people have open, bleeding sores that allow enough of the virus to pass from one person to another.
Can you tell if someone is contagious with mono?A person can have mononucleosis and not show symptoms for weeks. When symptoms do start, they are very mild in the beginning with, possibly, just a sore throat and fatigue or headache.
Can you spread a cold sore by touching it?Yes, you can pass on the herpes virus by touching a cold sore and then touching another person or a surface that someone else then touches.
10 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
By Ingrid Koo, PhD
Ingrid Koo, PhD, is a medical and science writer who specializes in clinical trial reporting
