I had a boyfriend who had some sort of STD about a year ago, but he assured me that his doctor declared him cured of the disease. I'm worried because we did some heavy petting and foreplay more than four months ago. It did not lead to actual penetration, but there were times when I felt some discharge from him on my genitals. Is it possible to contract an STD that way?

J.J.

This is a very complex question. As you probably know, STD stands for "sexually transmitted disease." While hepatitis B and C as well as other infections can be transmitted sexually, when most people refer to an STD they are talking about a group of a few infections such as syphilis, gonorrhea, chlamydia, trichomoniasis and herpes. Obviously, if your boyfriend had truly been cured of an STD, sexual contact with him did not put you at risk of acquiring that infection. However, you may be concerned that your boyfriend was misinformed or dishonest in that regard.

Generally speaking, with any STD, the less contact, the lower the risk of transmission. A woman's risk is considerably higher when there is contact with the inside of the vagina. That is because most infectious agents do not penetrate intact skin very well. The vaginal wall, however, is lined by mucous membrane, a barrier that is much thinner than skin and easier for organisms to invade. Microbes deposited inside the vagina may also pass through the cervix (neck of the uterus, or womb) to the uterus, where infection may be more likely still.

Keeping those facts in mind, let's examine your risk of various STDs. By far the most important infection transmitted sexually is HIV. HIV transmission through heavy petting and foreplay, with some discharge from the penis, would be somewhat unusual, but probably not impossible. However, if all you did with him was what you describe, I probably would not worry too much about getting HIV in that manner.

What about other STDs? Herpes is usually transmitted by contact with small blisters or sores. However, even if your partner had no visible sores, the disease could still be passed on to you. Again, contact with the vaginal wall would have increased your risk.

Gonorrhea and chlamydia are STDs that cause penile discharge in men and infection of the cervix in women. Unlike HIV and herpes, these diseases can be cured with antibiotics. However, the immune system is generally able to rid the body of these infections even without treatment (though untreated disease may cause serious complications, such as bloodstream infections, joint infections, prostate infections in men and pelvic inflammatory disease in women). I doubt you were at risk of gonorrhea or chlamydia from your exposure to this man. If he had one of these infections, even if he was not treated, he probably would not still be carrying these organisms by the time you were exposed to him eight months later.

Trichomoniasis is a mild STD that can cause vaginal discharge and irritation in women. It is easy to treat but sometimes difficult to get rid of, because patients are commonly re-infected by their partners. I wouldn't worry too much about your risk of trichomoniasis either, because it is usually transmitted by penetration.

Finally, syphilis is another important STD. Syphilis tends to be most contagious in the first few months after a person acquires the infection, but the disease could also be transmitted much later. Like gonorrhea, chlamydia and trichomoniasis, syphilis can be cured. If your partner was correct about that, then your risk of syphilis is nil. If your boyfriend had syphilis but was not adequately treated, then you may have been exposed. To be certain, you could get a simple blood test to rule out the disease. But, frankly, I wouldn't worry about it. I think your risk of acquiring any of these diseases is low, given that you never had intercourse and your exposure occurred eight months after your partner was apparently treated.

Your question highlights the importance of using condoms as an aid to peace of mind. If correctly used, condoms are effective birth-control devices, though not as effective as the pill. They can also prevent STDs. Some medical studies have shown that correctly used condoms are nearly 100 percent effective in stopping the spread of HIV. They are probably equally effective in preventing other sexually transmitted diseases.