Sexually Transmitted Diseases (STDs) are infections passed from one person to another primarily through sexual contact. These infections are caused by bacteria, viruses, or parasites, and they spread through the exchange of bodily fluids or through skin-to-skin contact. A common concern is whether intimate activities that do not involve traditional intercourse, such as kissing, can serve as a route for transmission. While kissing is a low-risk activity compared to other forms of sexual contact, it does involve the exchange of saliva and potential contact with skin lesions, meaning a few specific infections may be transmitted this way.
The Most Common STD Transmitted by Kissing
The most frequently transmitted STD through kissing is the Herpes Simplex Virus, specifically Type 1 (HSV-1), which causes oral herpes, often called cold sores. HSV-1 is extremely common, with a large percentage of the population exposed to the virus by early adulthood. Transmission occurs through direct skin-to-skin contact or contact with an infected person’s saliva.
The risk of transmission is highest when a person is experiencing an active outbreak, characterized by visible blisters or open sores. These lesions contain high concentrations of the virus. However, the virus can also be passed on during periods of asymptomatic shedding, when no visible sores are present. Asymptomatic shedding means the virus is replicating and being released onto the skin’s surface or into the saliva without causing any noticeable symptoms. While HSV-2 is typically associated with genital herpes, it can also be transmitted to the mouth and spread through kissing if an oral infection is present.
Rare Infections Transmitted Through Oral Lesions
While Herpes is the most common, other infections typically considered STDs can be transmitted through kissing, but only under specific circumstances involving active sores. Syphilis, a bacterial infection, is one such example.
Syphilis
Transmission through kissing is possible only if an active, highly infectious sore, known as a chancre, is present on the lips or inside the mouth of the infected individual. These primary chancres are often painless and can be small, yet they are teeming with bacteria. Deep kissing that involves contact with this lesion or with a secondary-stage oral lesion, called a mucous patch, can allow the bacteria to enter the partner’s body. Without the presence of an active oral sore, the risk of Syphilis transmission through kissing is negligible.
Human Papillomavirus (HPV) and Gonorrhea
Human Papillomavirus (HPV) may also be passed on through deep, open-mouth kissing, although this is not considered the primary route of transmission. Some studies suggest that the exchange of saliva and mucosal contact during deep kissing may play a role in oral HPV transmission. However, isolating kissing as the sole cause is difficult because individuals who engage in deep kissing often engage in oral sex, which is a proven, higher-risk activity. Newer evidence also suggests that Gonorrhea may be transmitted through the exchange of saliva during deep kissing, though this risk is still considered low.
Infections That Are Not Transmitted By Kissing
Many of the most commonly discussed STDs are not transmitted through kissing because they require specific biological conditions not met by the exchange of saliva.
HIV and Chlamydia
Human Immunodeficiency Virus (HIV), for instance, cannot be transmitted through saliva, as the virus is present in extremely low, non-infectious quantities. The virus is primarily transmitted through blood, semen, pre-seminal fluid, rectal fluids, vaginal fluids, and breast milk. For HIV transmission to theoretically occur during deep kissing, both partners would need extensive open sores or bleeding gums, allowing a significant amount of infected blood to enter the bloodstream, which is an extremely rare scenario. Similarly, Chlamydia is generally not transmitted by casual kissing. Chlamydia requires contact with infected genital, rectal, or pharyngeal secretions, and it is not carried in saliva in a transmissible quantity.
Hepatitis B and C
Hepatitis B and Hepatitis C, viral infections that attack the liver, are also not transmitted through kissing. Hepatitis B is primarily spread through blood, semen, and other body fluids, and transmission through kissing is not considered a viable route unless blood is involved. Hepatitis C is almost exclusively transmitted through blood-to-blood contact and is not passed through saliva or casual contact.