Sexually transmitted infections, often called STIs, are infections you can catch during sex. They are also called sexually transmitted diseases, or STDs. Most STIs are caused by bacteria or viruses.

The most common STIs include:

  • Chlamydia
  • Gonorrhea
  • Mycoplasma genitalium
  • Genital herpes, also called “herpes simplex virus” or “HSV”
  • Genital warts, also called “human papillomavirus” or “HPV” – Some types of HPV can cause cancer of the cervix, penis, or anus.
  • Hepatitis B
  • Syphilis
  • Trichomoniasis
  • Human immunodeficiency virus, also called “HIV” – This is the virus that causes AIDS.

Many of these infections can be transmitted through any type of sex. That includes not just vaginal or anal sex, but also oral sex and other types of sex play. HIV and hepatitis B can be transmitted in other ways, too, such as exposure to body fluids.

Hepatitis A and hepatitis C are other types of hepatitis viruses. They are usually transmitted in other ways, but can also be transmitted through sex.

Zika virus is usually spread through mosquito bites. But it can also be transmitted through sex.

STI screening includes a series of tests that doctors use to find out if a person has any STIs. STIs often don’t cause any symptoms. People can have STIs and not know it. That’s what makes screening so important.

Doctors recommend that people who are at risk for STIs be screened even if they have no symptoms and feel fine. For example, you could be at risk for chlamydia if you had unprotected sex with a new partner. Screening for chlamydia will alert your doctor if you do have this infection, so you can get treatment. Treatment will prevent the infection from getting worse and keep you from infecting other people.

There are different types of tests that screen for different infections. Many STIs can be found through a blood or urine test. If you decide to be screened for STIs, your doctor or nurse can work with you to figure out which specific tests you need.

Different screening tests are appropriate for different people, depending on their gender and sex habits.

  • All people (including teenagers) should get screened at least once for HIV.
  • All females younger than 25 years who have had sex should be screened every year for gonorrhea and chlamydia.
  • Females older than 25 who have sex with more than 1 partner and do not use condoms should be screened every year for gonorrhea and chlamydia.
  • Males who have sex with males should be screened at least once a year for HIV, syphilis, chlamydia, and gonorrhea. This should involve testing of any body parts that could be infected, including the rectum. Males who have sex with males should also be screened at least once for hepatitis A, B, and C.
  • Pregnant people should be screened for syphilis, HIV, and hepatitis B. They should also be screened for chlamydia and gonorrhea if they are younger than 25 years old or are having sex with more than 1 partner. Some pregnant people might also need to be screened for other infections depending on their sex habits.
  • All people who are infected with HIV should be screened at least once for hepatitis A, B, and C. They should also be screened at least once a year for syphilis, chlamydia, and gonorrhea. Females who are infected with HIV should be screened at least once a year for trichomonas. Males who are infected with HIV, and who have sex with males with HIV, should be screened at least once a year for hepatitis C.
  • Transgender and gender-diverse people should be screened based on their anatomy and sex habits.

The list above includes some general guidelines, but some people might need other screening tests depending on their sex habits and other factors. If you are unsure whether you should be screened and for what, ask your doctor or nurse for advice.

If you have a doctor or nurse you see regularly, they should be able to screen you. But if you prefer to have screening done without your regular doctor or nurse, or if you don’t have one, you can go to a clinic. To find a clinic near you, check with your local Department of Health or visit Some clinics let you get screened without giving your name (anonymously).

Be careful with any pharmacies or online stores that offer to sell you kits to use at home to screen for STIs. For some of these tests, you turn in or mail away a sample, and then you get the results either by phone or online. For others, you do a test at home and get results within an hour. But it is not always clear which test kits are ones you can trust. If you do use one of these kits and get a positive result, be sure to follow up with a doctor or nurse. And if you get a negative result but think you might have an infection, see a doctor or nurse.

In general, watch out for any genital itching, burning, sores, or discharge. But be aware that many STIs do not cause any symptoms. The best way to know for sure if you have an STI is to be screened.

If you have an STI, you will need treatment. The right treatment will depend on the type of STI you have. Treatment might include antibiotics or medicines called antivirals, which fight viruses. Treatment can cure your infection or keep it from getting worse. It can also reduce the chance that you spread your infection to others.

If you do have an infection, you might need to tell the people you could have infected. Your doctor or nurse can help you figure out which partners you need to tell based on when you last had sex with them.

There is no definite way to prevent all STIs. But there are things you can do to lower your chances of catching one:

  • The most important thing you can do is to use a condom every time you have sex. Both external (male) and internal (female) condoms can protect against STIs. But be aware that condoms made out of “natural materials,” such as sheep intestine, do not protect against STIs.
  • Ask your doctor if there are any vaccines you should get. If you are 26 years old or younger, you can get a vaccine to protect against HPV, the virus that causes genital warts and cervical cancer. Some older people can also get the HPV vaccine. If you do not have hepatitis A or B and have not already gotten the vaccine for hepatitis A or B, you can get those vaccines, too.
  • If your partner has herpes, they can reduce the chances of infecting you by taking a medicine called valacyclovir (brand name: Valtrex).
  • If you are at very high risk of catching HIV, you might be able to take a pill every day to reduce the chances that you will get HIV. If you are interested in this, talk to your doctor.