I'm trying to get a clear picture of the likelihood of getting an STD from oral sex and kissing. I am pretty consistent in using a condom for vaginal sex, but I almost never wear a condom when receiving oral sex, and of course there is a lot of skin to skin contact and fluid exchange from kissing. I am a male, and I'm concerned about three scenarios. First, for a man and woman kissing, if one person has an STD, what is the likelihood of one person giving that STD to the other person through kissing? Second, for a man receiving oral sex from a woman, if the woman has an STD, what is the likelihood of the woman giving the man that STD through giving him oral sex? Third, for a man giving oral sex to a woman, if the woman has an STD, what is the likelihood of the man getting that STD from the woman through giving her oral sex? Thanks in advance for your response.
Welcome to the STD forum. Responding first to the title you chose for your question: STDs are not transmitted by kissing. Some STDs, but not others, are possible through oral sex. Still, oral sex -- even if unprotected -- is a lot less likely to result in STDs than vaginal or anal sex.
Now I have read the question itself. First, don't feel unusual or embarrassed by not using condoms or other barriers for oral sex. Very few people do that. And although the STD risk aren't zero, they are low enought that for the most part it doesn't much matter. Oral sex, even unprotected, generally is in the safe sex category. Having said that, people who are nervous about it and want 100% protection should consider condoms for fellatio (oral-penile contact) and dental dams or a sheet of food wrap for cunnilingus (oral-vaginal).
To your specific questions:
1) Kissing carries no STD risk. Nobody can say it is zero, and rare cases of syphilis have been transmitted by kissing. And oral herpes can and usually is transmitted by kissing, but that's not considered an STD.
2) Unprotected fellatio can result basically in 3 STDs in men: Herpes due to HSV-1, if the oral partner has an active case of oral herpes; gonorrhea, which is uncommon but certainly happens; nongonococcal urethritis (NGU), which sometimes may be due not to an STD per se but to entirely normal oral bacteria. Of these, NGU is probably the most common; herpes and gonorrhea are rare. Chlamydia, HSV-2, and HPV are rarely if ever transmitted by oral sex. And syphilis is so rare anyway that it's not a serious consideration. There probably have been zero syphilis cases transmitted by kissing in the past few years (in the US).
3) Vaginal to oral STD transmission is really rare. There are theoretical risks for gonorrhea, herpes (HSV-2), oral HPV infection, and perhaps others -- but in my busy STD clinic (15,000 patient visits per year) we rarely if ever see such a case.
Here is a thread that gives some of the biological reasons that STDs are transmitted in certain ways but not others. Please read it, starting with the follow-up comments that begin December 14: http://www.medhelp.org/posts/show/1119533
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