Chlamydia (kluh-MID-ee-uh) is a common sexually transmitted infection (STI). You may not know you have chlamydia because many people never develop the signs or symptoms, such as genital pain and discharge from the vagina or penis.

Chlamydia affects both men and women and occurs in all age groups, though it's most prevalent among young women. Chlamydia isn't difficult to treat once you know you have it. If left untreated, however, chlamydia can lead to more-serious health problems.

Early-stage chlamydia infections often cause few or no signs and symptoms. When signs or symptoms occur, they usually start one to three weeks after exposure to chlamydia. Even when signs and symptoms occur, they're often mild and passing, making them easy to overlook.

Signs and symptoms of chlamydia infection may include:

• Painful urination
• Lower abdominal pain
• Vaginal discharge in women
• Discharge from the penis in men
• Painful sexual intercourse in women
• Bleeding between periods and after sex in women
• Testicular pain in men