Any sexually active person can get chlamydia, but it is most common among young people ages 14 to 24. In part, this is because some young people don’t use condoms as often as they should. Other reasons also make chlamydia more common in this age group. These reasons include behavior, biology, and culture. STIs are also called sexually transmitted diseases (STDs).

Oral contact can cause an infection of the mouth and throat. Vaginal contact can cause an infection of the urethra or cervix. Using a condom greatly reduces the chances of getting the infection, but it’s still not a guarantee. People with a history of unprotected sex, multiple sex partners, or both should get screened. Ejaculation does not need to occur to pass on the chlamydia bacteria. It can also be passed from a pregnant woman to her baby during childbirth. Some infants exposed to chlamydia get eye infections and pneumonia. Getting treated for chlamydia doesn’t mean you won’t get it again. You can be re-infected if you have sex with an infected partner.

Symptoms may appear within 1 to 3 weeks after exposure. When they do occur, symptoms include vaginal discharge or burning with urination in women. For men, the symptoms include penis discharge, burning during urination, and pain or swelling in one or both testicles. If the rectum is infected in men or women, rectal pain, discharge, and bleeding can occur.

The CDC says that studies showed only 1 in 10 men and up to 3 in 10 women with confirmed cases of chlamydia actually had symptoms. When symptoms do occur, they may not show up until weeks after an exposure The disease is easily curable if found early. If it goes undetected, it can cause infertility in men and women.

Untreated women can develop pelvic inflammatory disease (PID), and some women with PID will become infertile. Many women who develop PID will have chronic pain. PID can also lead to a life-threatening (ectopic) tubal pregnancy. Some women will also develop inflammation of the liver and the lining of the abdomen (peritonitis). Pregnant women with untreated chlamydia can have premature labor. Their newborn may have eye infections and pneumonia. Untreated men and women can also get reactive arthritis and an infection of the tubes that carry urine from the kidneys to the bladder (urethritis). They may also get an eye infection (conjunctivitis).

The CDC estimates that 1 in 20 sexually active girls and young women ages 14 to 24 can be infected with chlamydia. Behavior, culture, and biology contribute to this high number. The higher number may also point to the difficulty that young people have in getting STD services in the U.S. Reasons for this can be cost, stigma, and transportation.

Chlamydia usually does not cause symptoms. When it does in men, it causes inflammation of the male reproductive system near the testicles. Men can have a watery discharge from the penis and painful urination. The rectum can also be infected, causing rectal pain, discharge, and bleeding.

One study found that women with chlamydia are more likely to develop cervical cancer and to become HIV positive than women without the condition.

Sexually active men and women can be screened with a simple urine test. You should tell previous sexual partners if you are infected. Your healthcare provider can tell you how far back you need to go to notify partners. Since you can get re-infected, the best way to prevent infection is to not have vaginal, anal, or oral sex. You can also protect yourself by being in a long-term, mutually monogamous relationship with a partner who is not infected. You can reduce your risk by using a male latex condom correctly.