1. Does having another STI mean a person is at greater risk of HIV infection if they are exposed to HIV?

Yes. In particular, infections that cause sores on the genitals, such as chancroid and syphilis, increase a person’s risk of becoming infected if exposed to HIV. Other STIs also increase the risk of HIV infection.

2. Does using a condom only some of the time offer any protection from STIs, including HIV?

For best protection, a condom should be used at every act of sex, and used correctly. In some cases, however, occasional use can offer some protection. This depends on the risk of STI that the person is exposed to (which depends on the person’s and their partner’s sexual behavior, number of sexual partners, and the number of people infected in the same population group or geographic area). For people who are frequently exposed to STIs, including HIV, using a condom only some of the time will offer only limited protection.

3. Who is more at risk of becoming infected with an STI, men or women?

If exposed to STIs, women are more likely to become infected than men due to biological factors, because they have a greater area of exposure (the cervix and the vagina), and small tears may occur in the vaginal tissue during sex, providing a pathway for infection. All people who have anal sex are at greater risk of an STI for the same reasons.

4. Can STIs be transmitted through oral sex (mouth on penis or vagina)?

Yes. Herpes, syphilis, hepatitis B, HPV, chlamydia, and gonorrhea can be transmitted through oral sex.

5. Can STIs be transmitted through anal sex (penis in anus)?

Yes. STIs, including HIV, are commonly transmitted through anal sex. Unprotected anal sex carries the highest sexual risk of HIV transmission. The use of condoms with lubricants is the best way to protect against STIs during anal sex.

6. Will washing the penis or vagina after sex lower the risk of becoming infected with an STI? 

Genital hygiene is important and a good practice. There is no evidence, however, that washing the genitals prevents STI infection. In fact, vaginal douching increases the risk of acquiring STIs, including HIV, and pelvic inflammatory disease. If exposure to HIV is certain, the use of post-exposure prophylaxis (PEP) prevents HIV acquisition. If exposure to other STIs is certain, PEP for STIs should also be used.

7. How well do condoms help protect against HIV infection?

On average, among heterosexual couples, when one partner is HIV-positive and the other is HIV-negative, condoms offer at least 80% protection against HIV when used at every act of sexual intercourse. For insertive anal sex, condoms offer at least 63% protection, and for receptive anal sex, the protection is at least 72%. However, these estimates are based on self-reported condom use. They may, therefore, overestimate the true level of protection. 

The likelihood that a person who is exposed to HIV will become infected can vary greatly. The chance of infection depends on several factors:

  • Stage of HIV infection: The first weeks after a person becomes infected are when they are most infectious and it is likely their serostatus will not be known at this early stage of infection.      
  • Viral suppression by antiretroviral therapy (ART): There is no risk of HIV transmission if ART is taken properly and viral load has become undetectable.
  •  Type of sex act: Receptive anal sex confers the highest risk, followed by vaginal sex; transmission through oral sex is negligible.
  • Presence of other STIs: HSV-2 (genital herpes) increases the risk of HIV 3-fold, syphilis 2-fold and trichomoniasis 1.5-fold.
  • Male circumcision status: Male circumcision can reduce the risk of HIV infection by 50–60% among those who have vaginal sex with a female partner.