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What Are Sexually Transmitted Infections (STIs)?

A sexually transmitted infection (STI) is an infection that is spread during sex. An STI can also be called STD (sexually transmitted disease). You can become infected with an STI if you have sex with someone who has an STI. Any sex that involves the penis, vagina, anus, or mouth can spread these infections. Some STIs also spread through body fluids, such as semen, vaginal fluid, or blood. Others spread through contact with infected skin. The most common STIs are chlamydia, genital warts, genital herpes, syphilis, HIV, gonorrhea, and trichomoniasis.

Who is at risk?

Any person who has sex can get an STI. Your risk increases if:

  • You have more than 1 partner. The more partners you have, the greater your risk.

  • Your partner has other partners. If your partner is exposed to an STI, you could be, too.

  • You or your partner have had sex with other people in the past. Either of you might be carrying an STI from an earlier partner.

  • You have an STI. The STI may cause sores or other health problems that increase your risk for new infections. Your risk will stay high unless you are treated for your current STI and change the behaviors that put you at risk.

Prevent future problems

Left untreated, certain STIs can be very painful or can lead to cancer or, rarely, death. Some can harm unborn babies whose mothers are infected. Others can cause you to not be able to have children (sterility) or can affect changes in behavior or your ability to think. You can prevent these problems with safer sex, regular checkups, and early treatment. Always use a latex condom when you have sex. Get tested if you’re at risk. And get treated early if you have an STI.

Closeup of hands holding box of condoms.
Using a latex condom every time you have sex can reduce your risk of STIs.

Getting checked

The only sure way to know if you have an STI is to get checked by a healthcare provider. If you notice a change in how your body looks or feels, have it checked out. But keep in mind, STIs don’t always show symptoms. So if you’re at risk for STIs, get checked regularly. If you find you have an STI, have your partner get treatment. If not, their health is at risk. And left untreated, your partner could pass the STI back to you, or on to others.

Common symptoms

Be alert to any changes in your body and your partner’s body. Symptoms may appear in or near the vagina, penis, rectum, mouth, or throat. They may include:

  • Unusual discharge

  • Lumps, bumps, or rashes

  • Sores that may be painful, itchy, or painless

  • Itchy skin

  • Burning with urination

  • Pain in the pelvis, belly (abdomen), or rectum

  • Bleeding from the rectum

Even if you don’t have symptoms

You may have an STI even if you don’t have symptoms. If you think you are at risk, get checked. Go to a clinic or to your healthcare provider. If your partner has an STI, you need to be tested even if you feel fine.

Vaccines to prevent disease

Vaccines are available to prevent hepatitis A and hepatitis B. These are 2 kinds of STIs. There is also a vaccine to prevent human papillomavirus (HPV). This is a virus that can be passed from person to person through sexual contact. Ask your healthcare provider whether any of these vaccines is right for you.

Online Medical Reviewer: Amy Finke RN BSN
Online Medical Reviewer: Barry Zingman MD
Online Medical Reviewer: L Renee Watson MSN RN
Date Last Reviewed: 3/1/2023
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