A female gets chlamydia through sexual contact with an infected partner. Vaginal, anal, and oral sex can all transmit the bacteria, and using a condom significantly reduces the risk. About 75% of women with chlamydia have no symptoms, which means an infected partner may not know they’re carrying it.
How Chlamydia Spreads During Sex
Chlamydia is caused by a bacterium that lives in the mucous membranes of the genitals, rectum, and throat. It passes from one person to another through direct contact with these tissues during unprotected sex. Vaginal intercourse is the most common route for women, but anal and oral sex can also transmit the infection. The bacteria cannot survive long outside the human body, so you cannot get chlamydia from toilet seats, swimming pools, sharing towels, or casual contact like hugging.
What Happens Inside the Body
Once the bacteria reach the cells lining the cervix or other reproductive tissues, they attach to the cell surface and enter. Within about two hours, the bacteria shift into a form that can rapidly multiply. Over the next two to three days, the bacteria grow and divide inside the cell until it bursts open, releasing new infectious particles that spread to neighboring cells. This cycle repeats, and the infection can gradually move deeper into the reproductive tract if untreated, reaching the uterus and fallopian tubes.
Why Younger Women Face Higher Risk
The cervix has two types of surface cells. The outer portion is covered in tough, flat cells similar to the lining of your mouth. The inner canal is lined with softer, more textured cells called glandular cells. In adolescents and young women, higher estrogen levels cause those softer glandular cells to extend onto the outer surface of the cervix, a normal condition called cervical ectropion. These cells are more vulnerable to infection, which is one reason chlamydia rates are highest among women in their late teens and twenties. As women age, these cells gradually recede back into the cervical canal.
Rectal and Throat Infections
Women can get chlamydia in the rectum through receptive anal sex, but that’s not the only way. Research shows that rectal chlamydia rates are similar in women regardless of whether they report having had anal sex. The most likely explanation is auto-inoculation: bacteria from a vaginal infection spread to the rectal area on their own, through normal anatomy and contact. Studies have found that between 33% and 83% of women with a genital chlamydia infection also test positive for rectal chlamydia.
Throat infections are less common, with prevalence ranging from 1% to 3% in women tested at sexual health clinics. These infections are typically acquired through oral sex and often occur without any genital or rectal infection present.
Transmission During Childbirth
A pregnant woman with an active chlamydia infection can pass the bacteria to her baby during vaginal delivery. As the baby moves through the birth canal, it comes into contact with infected tissue. This can cause eye infections or pneumonia in the newborn. Prenatal screening catches most cases before delivery so they can be treated.
Why Most Women Don’t Know They Have It
Roughly three out of four women with chlamydia experience no symptoms at all. When symptoms do appear, they typically show up one to three weeks after exposure and may include unusual vaginal discharge, burning during urination, or bleeding between periods. Because the infection is so often silent, a woman can carry it for months without realizing, passing it to partners during that time. In 2024, nearly 944,000 chlamydia cases were reported in U.S. women alone, and the true number is likely higher due to undiagnosed infections.
If you’ve been exposed, a test can reliably detect the infection about one week after exposure and catches nearly all cases by two weeks.
Getting Chlamydia Again After Treatment
Having chlamydia once does not protect you from getting it again. The body does not build lasting immunity to the bacteria. Reinfection rates are notably high: studies have found that 18% to 34% of young women test positive again within months of completing treatment. Reinfection happens most often because a sexual partner wasn’t treated at the same time, meaning the bacteria pass back and forth. In some cases, a lingering rectal infection that wasn’t detected or treated can reintroduce the bacteria to the genital tract through auto-inoculation.
This is why both partners need to be treated simultaneously, and why retesting about three months after treatment is recommended even if symptoms have resolved.