Casual sex is more common than you might think. Up to 80 percent of college students report engaging in casual hookups. Plenty of older adults do, too. Men who have sex with men (MSM) in particular tend to have a higher number of sexual partners compared to heterosexual men and women.

If you regularly engage in casual sex or are considering having sex with multiple partners, you may want to know more about any risks involved, such as the risk of contracting a sexually transmitted infection (STI). Here are 5 things you should know about having casual sex with multiple partners.

Casual sex can increase the risk of contracting HIV. This is simply because the more sexual partners a person has in a lifetime, the more likely they are to have a partner who is HIV-positive. Using condoms and taking pre-exposure prophylaxis (PrEP) medication both dramatically reduce the risk of contracting HIV.

It’s also worth noting that 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 — lowers the risk of HIV transmission.

If you think you’ve been exposed to HIV, you should contact your healthcare provider as soon as possible. If you’re able to visit your healthcare provider within 72 hours of potential exposure, you may qualify for post-exposure prophylaxis (PEP). PEP is an antiretroviral treatment that can help reduce your risk of contracting HIV.

If you engage in casual sex, you might also consider discussing PrEP medication with your healthcare provider. PrEP is a daily medication that greatly reduces your risk of contracting HIV if you’re exposed.

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 your body and the type of test you’re taking.

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

Apart from HIV, casual sex increases the risk of contracting other STIs, such as herpes, syphilis, gonorrhea, chlamydia, and certain types of hepatitis.

According to the Centers for Disease Control and Prevention (CDC), over 2 million new STI cases occur in America every year. Half of those cases affect young people ages 15 to 24.

If left untreated, STIs can lead to a variety of medical issues, including infertility, damage to organs like your heart and kidneys, pregnancy complications, and cancer.

Using condoms significantly reduces the risk of contracting an STI.

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, especially in women. This means they can go undiagnosed for a long time, which can increase the risk of complications from these conditions.

You can be tested for nearly all STIs with a trip to see your healthcare provider, or at a sexual health clinic. For women, HPV is not included in general STI tests, but it can be performed along with regular cervical cancer screening (pap smears).

The CDC has recommendations for STI testing based on factors like age and sexual orientation. In general, the CDC recommends:

  • All adults and adolescents, ages 13 to 64, be tested for HIV at least once.
  • All men who have sex with men (MSM) be tested at least once yearly for syphilis, HIV, chlamydia, and gonorrhea. For those who have multiple partners or anonymous partners, be tested for all the STIs listed here once every three to six months.
  • All women who are sexually active, age 25 or younger, be tested for gonorrhea and chlamydia annually. Women who are over 25 and have multiple partners should continue to be tested yearly.
  • All women who are pregnant be tested for HIV, syphilis, and hepatitis B in early pregnancy. Pregnant women at risk of chlamydia and gonorrhea should also be tested for those conditions.

Keep in mind, these are minimum recommendations. If you have multiple casual sexual partners, your healthcare provider may recommend you get tested for STIs, including HIV, every three months or more.

If you enjoy sex with multiple partners, take steps to care for your health by using condoms and having regular STI testing. You may also consider preventive medications to reduce your risk of HIV.

Remember, if you think you may have been exposed to HIV or an STI, make an appointment with your healthcare provider right away. They may recommend preventive medication and discuss timing for you to be tested.