The usual advice about HIV infection risk mentions increased risk for those giving oral sex if they have gum disease, mouth sores, etc, on the basis that HIV-infected cum/precum could get past the oral barrier and into the bloodstream.

Doesn't that then also imply a risk from kissing, since if both parties have less than perfect oral health, there is a risk that one person's small bleed could infect the other person through their impaired oral barrier (if the first person has untreated HIV)?

Gingivitis/periodontal disease, mouth sores/ulcers, tongue bites or fissures, chapped/cracked lips, a shaving cut near the lips - none of these things are uncommon.

If your view is, "These scenarios are all zero risk", can you explain why in scientific terms?

I'm trying to get to a point where I can kiss a new person whose up-to-date HIV status I don't know with certainty, and not then worry for weeks afterwards if I realise I have a cut on my lips, a mouth sore that bleeds when nudged, etc.

There certainly seems to be a logical inconsistency for reasons you state:  all the factors you mention seemingly imply risk of HIV transmission by oral contact, especially sexual (prolonged, open mouth) kissing. However, the countervailing truth is that very few if any persons who have HIV (or overt AIDS) give kissing as their only potential risk for exposure and infection with HIV. In other words, in the sexual realm, virtually everyone with HIV has had high risk sex other than kissing -- typical anal or vaginal intercourse -- with a high risk or known infected partner in the few weeks before HIV made its appearance. Of course many (probably a large majority) of those events included kissing, and it isn't possible to know if vaginal or anal intercourse or the kissing component was the precise mechanism of virus transmission. And of course it's also possible that a person who had say ten different sexual exposures in the preceding weeks might have had intercourse in 8 of those events and only kissing during the other two. But if all 10 of those partners aren't available to test and know the source, it's not possible to know which event was responsible. The same is true of oral sex, i.e. fellatio, cunnilingus, or analingus (oral-penile, oral-vaginal, and oral-anal contact, respectively.

Still, if any of these types of exposure were significant risks for HIV, surely there would be at least some HIV infected persons who only had such exposures during the plausible transmission interval. But such cases are entirely or nearly absent.

When addressing kissing or oral sex exposures on this forum, in general we are careful to use such qualifiers as "little or no" risk, "virtually" no risk, and so on. But sometimes it's simpler and/or best meets the needs of the questioner to just say "no risk". In fact, it's impossible to prove a negative:  I can't prove the sun will rise tomorrow, but surely there is little chance it won't happen. Likewise, I can't say oral-oral HIV transmission doesn't or can't happen, but I am confident it is extraordinarily rare.

We can also speculate about possible biological reasons for the apparent difference in risk. They include the fact that saliva is known to inhibit or even kill HIV (for which reason saliva contact -- e.g. spit in the eye, shared drinking glasses, etc -- are no apparent risk. Also, in general oral exposure may be low risk because stomach acid inhibits or kills swallowed HIV. The types of cells susceptible to HIV may be less prevalent in oral tissues than deep in the genital tract. And the amount of HIV in semen or vaginal fluids is very high, whereas it is low in saliva and oral fluids. In general, there isn't much research on such biological details -- precisely because the exposure risk is so low that such studies are not considered a high priority.

Would I knowingly have open mouth kissing or oral sex with a known infected partner? Or one at especially high risk, like a man who has multiple male partners? Absolutely not. But If I were still in my dating years (as someone who only has sex with women), I really wouldn't worry about kissing and not so much about oral sex, whereas I would be very careful about partner selection and condom use for vaginal or anal sex.

Does that help sort things out for you? Let me know if anything isn't clear.

HHH, MD

That is helpful, thx.

A couple of follow-up points and a bonus point if I may:

1) Blood in the mouth is very common -- think of all the people at any point in time with inflamed gums, tooth bites of their cheeks, recent tooth extractions, and other causes. Millions (billions?) of people with HIV or at risk must have kissed or had oral sex in their presence -- yet still no reported HIV transmissions.

2) The stated approaches to partner selection and sexual safety are excellent protection against HIV, but you know as well as I do (perhaps a lot better) that these ideas often are impractical, because of varied personalities, sex drive altering judgment, basic truthfulness, and so on. As for kissing men I didn't know (if I were having sex with men), I just stated a common sense position that might not be appropriate for you or most people. I also wear seat belts and keep the batteries up to date in my smoke alarms even though the chance I'll be in a major auto wreck or house fire are low. It's a question of how far to press one's luck, which is -- you surely understand -- all over the map between different people. (Some idiots play Russian roulette for money!) Assuming you're in the dating scene but inherently careful and sexually conservative -- as I believe from our discussion so far -- is would say a) always discuss mutual HIV status before any intimate contact (infected people rarely lie when asked directly); b) avoid sex with known infected persons not on effective HIV treatment; c) use condoms for anal sex, both top and bottom; d) if such events are relatively frequent, take HIV drugs for pre-exposure prophylaxis (PrEP); and finally e) if sex will sometimes be unprotected despite your best attempts, speak with your doctor about doxy-PEP (post-exposure prophylaxis with a single dose of the antibiotic doxycycline for effective syphilis and chlamydia protection). [These are the basic guidelines for all men who have sex with men in most settings world wide -- your personal needs probably are different.]

3) In theory, inflammation of any kind involving exposed anatomic sites elevates the risk of HIV if exposed. For example, having genital HSV2 roughly doubles the risk. But "double" doesn't mean much if the risk is only one chance in a million, perhaps a figure relevant to insertive oral sex:  double that risk means one chance in 500,000. So here too, it's a matter of common sense:  I'd generally try to assure my balanitis is controlled prior to such an exposure, but if an opportunity otherwise seems right, I wouldn't lose a lot of sleep afterward.

If I may make use of my second follow-up:

2. Reports of single cases of any medical event usually are published precisely because they are rare. Health professionals do not need reminders of common, everyday situations or conditions. Of course I don't recall this particular report (26 years ago!). That kissing was a likely source of a single infection supports my statement above: "I can't say oral-oral HIV transmission doesn't or can't happen, but I am confident it is extraordinarily rare."

3. Exactly the same sort of analysis:  Yes this is biologically plausible, but since there few if any no known cases of HIV transmission by hand-genital contact, what does it matter?

That concludes this thread. My closing advice is that your apparent in-the-weeds web searching likely is only enhancing your worries. Anxious persons tend to seek or otherwise are drawn to information that magnifies their fears while missing the reassuring information that also is easily found. I suggest you stop; it doesn't seem worth it. I do hope this discussion has been helpful. If you remain concerned, I suggest you carefully re-read my replies above. 

Best wishes and stay safe.