Despite all I have read concerning this matter, I'm still rather confused and concerned, always trying to better understand the risks of such exposures. Yes, I have read that wearing a condom during vaginal sex with any CSW is considered safe for HIV and most of the STIs, but my concern is more about skin-to-skin transmissible infections during protected sex. Let me be more precise. 

When the bottom of the penis (not covered by condom) comes to contact with the vagina, is there potential risk for such STIs as Herpes Syphilis, HPV, etc? 

Does the transmission depend on how vigorously the rubbing happens?   

What if there are NO visible open Syphilis sores or Herpes outbreaks on the woman's vagina? Does it mean the risk is zero?  

One last question? Is there a potential risk that Herpes or Syphilis may be transmitted to a finger while fingering a vagina if there are no cuts or open wounds in the finger?  

Thanks so much in advance for your valuable clarifications on these and with admiration for your amazing work. 

Intact skin is a highly effective barrier to most infections, including herpes and syphilis, for which it has long been known that micro-injury is typically required for infection to take hold. For example, in animal experiments of syphilis and herpes, simply placing the causative agent on intact skin never results in infection; vigorous rubbing, often to the point of obvious redness or even scant bleeding, is required. In addition, we know that the initial lesions of genital herpes and syphilis occur predominantly at sites of maximum friction during sex. Genital skin probably isn't any more susceptible than skin elsewhere, except that it's a bit thinner -- and in women, moist tissues probably require less vigorous inoculation (which one reason women genrally are at higher risk for STDs than men are). HPV has not been well studied in the same way, and transmission might not always require such vigorous inoculation -- but we really don't know for sure.

To your specific questions:

1) Exposure of penis not covered by condom: Small risk, for ther reasons above.

2) More vigorous probably means more risk.

3) For syphilis, absence of visible sores markedly reduces the risk of transmission. Less so for herpes or HPV, for both of which asymptomatic lesions and viral shedding are common.

4) While one might assume a potential risk of transmission by fingering or other hand-genital contact, in practice it seems to virtually never occur. In 30 years in a busy STD clinic, I never saw a patient with genital herpes, syphilis, or HPV whose only possible contact was hand-genital exposure.

My last general advice is to follow safe sex practices, which means consistent condom use for penile-vaginal or -anal penetration with new or potentially unsafe partners, but otherwise not to worry about it. And for sure don't focus on the biological reasons for low risk. The important fact is that condoms work very well, if not quite perfectly. Unless somone is planning on a truly permanent, mutually monogamous sexual lifestyle -- which I do not recommend -- there will always be small risk of STD (although mostly from condom breakage or improper use). It's a fact of life, but not one that should be permitted to seriously interfere with love, romance, and rewarding sex.

I hope this has helped. Best wishes and stay safe--    HHH, MD

I thank you so much for such a satisfactory and reassuring reply. It's an honor coming from you, whose work I admire so. Unfortunately, there seems to be so much ignorance and prejudice around these topics, and the Internet appears more representative of misinformation than real facts. 

Again, your scientific explanations were powerful in clarifying why the risk of certain STIs is so tiny. 

Just a couple of questions, to make sure I understood two of your points correctly:

4) Potential risk of transmission by fingering or other hand-genital contact: 

In this case I was actually referring to the risk of contracting any skin transmissible diseases through the finger actually. Could Herpes of Syphilis infections travel to a finger that goes inside the woman's vagina?

Many thanks again! 

1) "ANY" risk? Sure. Condoms slip and secretions sometimes get inside, and nobody can say there is zero risk of transmission for any single sexual exposure, with or without a condom. But the risk in this situation would be extremely low and would generally not warrant either testing or worry.

4) My reply was intended to include transmission of STDs to the finger itself; sorry that wasn't clear. Again, it is not possible to say there is zero risk, and in the pre-antibiotic era (and back when latex gloves were not routinely used) syphilis of the fingers was an occasional occupational risk in dentists and physicians after coming in contact with patients' syphilitic lesions. And I suppose the rare herpetic whitlow could be acquired by fingering. But again, these are very rare and not worth either worry or testing.

When you wrote that "Condoms slip and secretions sometimes get inside," did you imply that the risk would occur only if the secretions should enter the penis urethra?

You cannot expect 100% protection from any safety device, sexual or otherwise: people die in auto accidents and plane crashes despite wearing seat belts. As I suggested above, disregard the biological reasons why condoms aren't perfect. The important thing is that condoms markedly reduce risk. But because no protection is 100%, even consistent condom users a) necessarily take some risk of STD from new or non-monogamous sexual contacts (and put their regular partners at risk); and b) therefore should still get occasional STD/HIV testing. This is all pretty common sense and obvious, it seems to me!