From Cory Silverberg,
Your Guide to Sexuality.
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It’s hard for researchers to determine how risky oral sex is since most people who engage in oral sex also engage in other sexual behaviors, making it impossible to know the way that an STD was transmitted.

That said, there are several STDs that can be transmitted via oral sex, including:

• Chlamydia
• Gonorrhea
• Herpes
• HIV
• Human Papilloma Virus (HPV)
• Nongonococcal urethritis (NGU)
• Syphilis
• Yeast infections

Chlamydia and oral sex

Oral sex is not considered a common cause of Chlamydia infection, but it is a possibility. If the vagina, cervix, anus, penis or mouth come in contact with infected secretions or fluids, then transmission is possible.

Gonorrhea and oral sex

Gonorrhea can be passed during oral sex (either giving or receiving). Ejaculation does not have to occur for gonorrhea to be transmitted or acquired. Gonorrhea survives well in the throat, and gonorrhea throat infections from oral sex are relatively common.

Herpes and oral sex

Herpes can be transmitted via skin to skin contact, so the risks during oral sex are clear. It’s important to remember that transmission can occur even if there are no visible sores, and you or your partner may be infected with herpes and not know it. Some people are not aware that cold sores are a form of herpes.

HIV and oral sex

While the risk is considered to be low, there have been documented cases of HIV transmission where the most likely way it was transmitted was through oral sex via semen, vaginal secretions or blood. HIV is not transmitted via saliva, and deep kissing is considered a safe sexual behavior. There have been cases of oral sex transmission during fellatio (performing oral sex on a man) and cunnilingus (performing oral sex on a woman).

HPV and oral sex

Oral sex is considered a less common cause of HPV infection, although it has been documented. HPV virus is shed from the surface of warts and any form of direct physical contact may result in transmission.

NGU and oral sex

Most of the germs that cause NGU can be passed during oral sex, even if the penis or tongue doesn’t go all the way into the vagina, mouth, or rectum, and even if body fluids are not exchanged. A recent Australian study provided further evidence for oral sex as a transmission route for NGU.

Syphilis and oral sex

Oral sex is considered an efficient way to transmit syphilis, with one CDC study reporting that over 13% of syphilis cases in a geographic area were attributed to oral sex. Transmission usually occurs during vaginal, anal or oral sex when syphilitic sores or patches come into contact with slightly abraded skin or mucous membranes.

Yeast infections and oral sex

There is evidence to suggest that women who have recurrent yeast infections may be infected by receiving oral sex. In one study receiving oral sex had an association with increased risk of recurrent yeast infections at a three times higher rate. Oral sex with someone who has a yeast infection can lead to thrush, which is a yeast infection in your throat. Oral contact with yeast will not give you a yeast infection in your vagina, because the yeast will be killed in your digestive system.