Although the risk is generally slightly less to the reciever of oral sex (it is the one performing it who is at a greater risk of contracting something from the reciever, no matter if it is two men or two women, or man performing oral sex on a woman...) the risk to the both parties is still very real.
All major STIs can be trasfered during oral sex, as adviceman listed them. His information regarding HIV is slightly out of date however - it is now well established that HIV can be transfer during oral sex to either party. Oral sex is, stastically speaking, slightly less like to lead to HIV infection that vaginal sex or anal sex, but the risk is still very real to both participants. [ Razhie's advice column | Ask Razhie A Question ]
adviceman49 answered Wednesday June 8 2011, 9:25 am: Having unprotected oral sex (giving a blow job without a condom) is risky. Some of the disease that can be transmitted through oral sex if your partner is infected include herpes, genital warts, gonorrhea, chlamydia, and syphilis. The risk of HIV transmission through oral sex is still undetermined. Some experts say there is little to no risk of getting HIV through fellatio, while some say there is possible risk, especially if there are cuts or sores in the mouth of the person performing oral sex.
Because most of the STDs mentioned are transmitted through contact with sores or lesions on the genitals, or are present in the pre-ejaculate fluid (precum), a person performing unprotected oral sex on an infected partner has already been exposed even before their partner ejaculates. If your partner cums in your mouth, you may be exposed to additional quantities of STD pathogens in the semen, which can infect you through the mucous membranes in your mouth and throat or through small cuts or scrapes on the inside of the mouth.
The above information was taken directly from the website for which I have supplied a link to below.
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