Whether a person is having sex with one new partner or multiple new partners, it’s natural to have questions about the risk of contracting or transmitting HIV during sex. Having questions about other sexually transmitted infections (STIs) is common, too.

STIs can pass between partners during any type of sexual activity. It’s possible to have an STI, including HIV, and have no symptoms.

That’s why getting tested for HIV and other STIs is so important. Even if an STI has no immediate symptoms, it could lead to serious health problems if it’s left untreated.

Here are seven things everyone needs to know about how HIV and other STIs can be transmitted during sex, and what types of activities may affect the risk.

A person can only transmit HIV if they already have the virus and their viral load isn’t suppressed by medication.

Only some kinds of bodily fluids can transmit HIV. Specifically, those bodily fluids are blood, semen, vaginal fluid, anal fluid, and breast milk. HIV can potentially be passed during sexual activities that involve these fluids.

However, certain types of sex pose a higher risk for HIV transmission.

HIV is more likely to be transmitted during anal sex than other types of sex because the lining of the anus is prone to rips and tears. This makes it easy for HIV to find an entry point into the body.

HIV can also be transmitted during vaginal sex. The vagina is less prone to rips and tears than the anus, but HIV can still be transmitted this way.

Oral sex is generally considered a very low-risk activity for HIV transmission. It’s still possible for HIV to be transmitted this way, particularly if a person has open sores or cuts on their mouth or genitalia.

For all types of sex, using condoms — or, where applicable, dental dams — dramatically lowers the risk of HIV transmission.

Accidental exposure to HIV during sex can happen. If it happens, it’s important to contact a healthcare provider as soon as possible.

Within 72 hours of potential HIV exposure, a healthcare provider may prescribe a type of medication called post-exposure prophylaxis (PEP). PEP is an antiretroviral treatment that can help reduce the risk of contracting HIV after an exposure. PEP usually consists of 3 different medications active against HIV combined into 2 pills and is usually taken for 4 weeks.

For anyone who is at increased risk for HIV, pre-exposure prophylaxis (PrEP) may be an option. PrEP is a daily medication that greatly reduces the risk of contracting HIV.

For example, U.S. federal guidelines state that PrEP should be considered for anyone who is HIV-negative and who is in a continuing sexual relationship with a partner who is HIV-positive. PrEP may also be considered for some people who aren't in a mutually-monogamous relationship with a partner who recently tested negative for HIV.

A healthcare provider can discuss how PrEP works and who may benefit from it.

The “window period” for HIV testing refers to the time between a person’s exposure to the virus and the point when an HIV test will detect the virus. This window period is different depending on an individual’s body and the type of test used.

In general, the window period is typically 10 days to 3 months. However, even if a person tests negative for HIV at 1 month, their healthcare provider will likely recommend another test at 3 months if that person has had a recent exposure or remains at increased risk for HIV.

According to the U.S. Centers for Disease Control and Prevention, the risk of contracting HIV may increase with the number of sexual partners a person has. This is because the more sexual partners a person has in a lifetime, the more likely they are to have a partner who is HIV-positive and whose viral load isn’t suppressed.

In the same way, the risk of contracting other STIs — such as herpes, syphilis, gonorrhea, and chlamydia — may also increase.

Regular HIV and STI testing can help minimize this risk. Get tested before and after each new sexual partner. Ask any new sexual partner to do the same.

Using condoms or dental dams during sex reduces the risk of transmitting HIV and other STIs. That’s because these barriers help prevent the exchange of bodily fluids that could carry HIV, other viruses, and bacteria.

HIV can’t be transmitted via skin-to-skin contact. However, other types of STIs can spread this way.

The only STIs that can be transmitted through skin-to-skin contact are:

  • herpes
  • human papilloma virus (HPV)
  • syphilis

Condoms and dental dams still help reduce the transmission risk of these STIs. That’s in part because barriers help minimize skin contact. But condoms and dental dams can’t eliminate the risk of these STIs completely.

A healthcare provider can discuss options to help reduce the risk of contracting these STIs and how to schedule regular STI testing.

Certain STIs don’t have any immediate symptoms, or may not have symptoms in some people at all. For example, human papilloma virus (HPV), chlamydia, and gonorrhea often don’t have symptoms right away. This means they can go undiagnosed for a long time, which can increase the risk of complications from these conditions.

If left untreated, STIs can lead to serious medical issues. In some cases, untreated STIs can cause infertility, damage to organs like the heart and kidneys, pregnancy complications, and cancer, among other conditions.

Testing for nearly all STIs is available with a trip to a healthcare provider or a visit to a sexual health clinic.

Taking preventive steps can reduce the risk of transmitting HIV and other STIs. It’s important to:

  • Get tested regularly for HIV and other STIs. Everyone should be tested at least once in their life, and then annually or more often if they are at increased risk.
  • Use condoms or dental dams during any type of sex where specific bodily fluids — semen, vaginal fluid, anal fluid, breast milk, or blood — may be exchanged. This includes anal sex, oral sex, vaginal sex, and potentially other sexual activities.
  • Use water- or silicone-based lubricants so that it’s less likely that a condom will break. Don’t use lubricants that contain baby oil, lotion, or petroleum jelly, since these can damage condoms.
  • Learn how to use condoms and dental dams. You can ask a healthcare professional or follow this helpful condom guide.
  • If a condom, or other barrier method, breaks or slips during sex, see a healthcare professional. If there’s a chance of an accidental HIV exposure, go within 72 hours and ask if PEP is an option.
  • Be open with healthcare providers about sexual history and sexual practices. They can discuss realistic ways to reduce the risk of STIs, including options like PrEP, the HPV vaccine, and the hepatitis A and B vaccines.

Many people wonder how often they need to be tested for HIV and other STIs. That depends on many factors, including individual sexual practices. It’s important for everyone to find a healthcare provider who helps them feel comfortable talking about sexual health.

For example, sometimes people don’t use condoms or other barriers during sex with new partners who haven’t recently been tested. In those cases, a healthcare provider may suggest more frequent testing for HIV and other STIs.

For some people, getting tested every 3 months may be the best approach. For others, yearly or less frequent testing may be enough.

It’s possible to take steps that help prevent HIV and other STIs from being transmitted. Using condoms and dental dams consistently can reduce the risk of transmission.

It’s also important to get tested for HIV and other STIs. A healthcare provider can provide individualized advice on how often it makes sense to get tested. It’s best to get tested before and after every new sexual partner.