How likely is it for someone who is carrying HIV to infect someone else through oral sex? Is the risk different depending on who is giving and who is receiving the oral sex? What about anal sex -- is the risk different depending on who is performing on whom? Does it make a difference if the recipient of anal sex is a man or a woman? And is kissing a medium for HIV transmission?

Fox

These are common questions in my medical practice. Let me start by saying that while it is not hard to prove that a particular act is dangerous, it is very difficult to prove that something is completely safe. For example, it is highly unlikely that insects such as mosquitoes could ever transmit HIV from one person to another. There has not even been a hint that HIV has ever been transmitted to someone in this way. However, it is impossible to prove that insect-borne transmission could never, EVER happen. All I can tell you is that there is no scientific evidence that insects pose a risk.

That said, we do know that certain sexual practices are riskier than others. As a rule, fluid containing the virus has to be transferred from one person to the other. Because HIV infects a type of immune cell, the virus also has to get into the recipient's body so that it reaches his or her immune system. Just spilling blood or another contaminated substance onto a person's intact skin is unlikely to get the virus into immune system cells. HIV can reach the immune system through breaks in the skin and across mucus membranes such as the mouth, the lining of the vagina and the male urethra (opening in the penis).

The other factor that matters in HIV transmission is the amount of virus present in the fluid that is transferred. For example, an HIV-positive patient will have virus in the saliva, but the amount is so small that saliva is not a common means of spreading HIV. Kissing is a very rare method of transmission, as are human bite wounds.

Greater amounts of virus are found in semen and vaginal secretions, and so practices that put one in contact with these fluids are riskier. Both men and women can become infected through heterosexual intercourse. It has been said that men are less likely than women to become infected through vaginal intercourse. This may be true, but the difference is not great enough to be important. Around the world, the most common means of transmission of HIV is through heterosexual sex. By far.

Oral sex can also transmit the virus. It is assumed that fellatio (oral sex performed on a man) is more likely to transmit HIV to the person who performs oral sex than to the man who receives it. This is especially true if there is ejaculation into the mouth and if the performer has any open sores in the mouth. Fellatio is probably not as risky as vaginal intercourse, however.

Oral sex performed on a female may be one of the least risky sex acts. While we cannot say that it never results in HIV infection, it occurs less often than in the other practices.

Anal sex, on the other hand, is a very efficient means of transmitting the virus. The recipient is at highest risk. There is usually at least minor trauma to the recipient's tissues, and there is often trauma to the other partner, and even bleeding There is no reason to think it makes a difference whether the recipient of anal sex is a man or a woman.

In summary, every sexual practice other than masturbation carries some risk of transmission of HIV. The risk increases with more exposure to more semen or vaginal fluids and more damage to the tissues. Condoms can minimize the risk, but they do not eliminate it.