Women get chlamydia through sexual contact with an infected partner. The bacteria that causes the infection, Chlamydia trachomatis, spreads during vaginal, anal, or oral sex without a condom. Roughly 70% of women with chlamydia have no symptoms at all, which means many people unknowingly pass it to their partners.
Sexual Contact Is the Primary Route
Chlamydia spreads through direct contact with infected genital, anal, or oral secretions. For women, the most common route is unprotected vaginal sex. During intercourse, the bacteria targets the cells lining the cervix, where it attaches, enters the cells, and begins reproducing. This process can happen with a single sexual encounter.
Anal sex is another well-established route. Women can develop a rectal chlamydia infection from receptive anal sex, or the bacteria can spread from the vagina to the rectum on its own without any anal contact at all. Oral sex carries risk too. Giving oral sex to a partner with a genital or rectal infection can lead to chlamydia in the throat, though throat infections may cause fewer problems than genital or rectal ones. Because most people who have oral sex also have vaginal or anal sex, it is difficult for researchers to isolate the exact risk from oral contact alone.
You Can’t Get It From Toilet Seats or Casual Contact
Chlamydia trachomatis is a fragile organism. It can survive on surfaces for two to three hours under humid conditions, but that brief window does not translate into a realistic transmission risk. You cannot catch chlamydia from a toilet seat, a swimming pool, sharing towels, hugging, or casual skin-to-skin contact. The bacteria requires the warm, moist environment of mucous membranes (the lining of the vagina, rectum, or throat) to infect a new host. Transmission is essentially limited to sexual activity and childbirth.
Mother-to-Baby Transmission During Birth
A pregnant woman with an untreated chlamydia infection can pass the bacteria to her baby during vaginal delivery. As the infant moves through the birth canal, it comes into contact with infected tissue. This can cause eye infections or pneumonia in the newborn. Routine prenatal screening exists specifically to catch and treat chlamydia before delivery.
Why Most Infections Go Unnoticed
Up to 70% of women with chlamydia experience no symptoms whatsoever. When symptoms do appear, they typically show up one to three weeks after exposure, though some women don’t notice anything for months. The most common signs include unusual vaginal discharge, a burning sensation during urination, and bleeding between periods or after sex.
The silent nature of chlamydia is what makes it so widespread. A woman can carry the infection for months or even years without knowing, during which time she can pass it to new partners. Left untreated, the bacteria can travel from the cervix up into the uterus and fallopian tubes, potentially causing pelvic inflammatory disease, chronic pain, and fertility problems.
Who Is Most at Risk
Chlamydia is most common among younger women. National survey data from the CDC found that sexually active females aged 14 to 24 had an overall chlamydia prevalence of 4.7%, compared to 1.1% among women aged 25 to 39. Biological factors play a role: the cervix in younger women has more of the cell type that chlamydia preferentially infects, and those cells become less exposed as the cervix matures.
Beyond age, specific behavioral factors raise risk. These include having a new sexual partner, multiple partners, a partner who has other concurrent partners, inconsistent condom use outside a mutually monogamous relationship, or a previous STI. The CDC recommends annual chlamydia screening for all sexually active women under 25, and for older women with any of these risk factors. If you test positive and get treated, retesting about three months later is recommended because reinfection is common.
How Condoms Reduce Transmission
Consistent, correct condom use reduces chlamydia transmission by more than 90%. External (male) condoms create a barrier that prevents the bacteria in genital secretions from reaching a partner’s mucous membranes. The key word is “consistent.” Using condoms most of the time still leaves gaps in protection, especially since an infected partner will look and feel perfectly normal the vast majority of the time. Internal (female) condoms offer similar barrier protection for vaginal sex. For oral sex, dental dams reduce direct contact with infected tissue, though they are used far less frequently in practice.
Because chlamydia is easily cured with antibiotics and causes no symptoms in most women, regular screening is just as important as condom use for prevention. Catching an infection early, before it has time to cause damage or spread to others, is the most practical line of defense.