A woman gets chlamydia through sexual contact with an infected partner. The bacteria pass from one person to another during vaginal, anal, or oral sex, even when the infected partner has no visible symptoms. In fact, about 75% of women with chlamydia never develop symptoms at all, which is why the infection spreads so easily and often goes undetected for months.
How Chlamydia Spreads During Sex
Chlamydia is caused by a bacterium that targets the cells lining the reproductive and urinary tracts. During vaginal sex, the bacteria transfer through direct contact between infected genital tissue and the cervix or urethra. This is the most common route of transmission for women. Condomless sex carries the highest risk, but transmission can still occur with inconsistent condom use or if a condom slips or breaks.
Anal sex is another transmission route. The bacteria can infect the lining of the rectum, and rectal chlamydia often produces no symptoms. Oral sex carries a lower but real risk, potentially leading to a throat infection that, again, usually causes no noticeable problems.
You don’t need to have intercourse to completion for transmission to happen. Any genital-to-genital contact or exchange of sexual fluids can transfer the bacteria. Shared sex toys that aren’t cleaned between uses can also pass the infection from one partner to another.
Why Most Women Don’t Know They Have It
The reason chlamydia is sometimes called a “silent” infection is that three out of four women who contract it experience no symptoms whatsoever. When symptoms do appear, they typically show up several weeks after exposure. That long, quiet gap means a woman can carry and transmit the infection without any clue something is wrong.
When symptoms do surface, they can include unusual vaginal discharge, a burning sensation during urination, bleeding between periods, or pain during sex. These signs overlap with several other conditions, so women who do notice something off may not immediately connect it to chlamydia.
What Happens Inside the Body
Once the bacteria reach the cells lining the cervix or urinary tract, they attach to the cell surface and enter within hours. Inside, they shift into a form that rapidly multiplies, creating clusters of new bacteria that eventually burst from the host cell and spread to neighboring tissue. This cycle of invasion, multiplication, and spread is what drives the infection deeper into the reproductive tract if it goes untreated.
Left unchecked, chlamydia can travel from the cervix up into the uterus and fallopian tubes, causing pelvic inflammatory disease. This can lead to chronic pelvic pain, scarring of the fallopian tubes, and fertility problems. The damage can happen gradually, sometimes before a woman even realizes she’s infected.
Can You Get Chlamydia Without Having Sex?
Chlamydia is not spread through casual contact. You won’t catch it from sharing a toilet seat, swimming pool, towel, or from hugging or kissing. The bacterium that causes sexually transmitted chlamydia is fragile outside the human body and requires direct contact with infected mucosal tissue to establish an infection.
There is one important non-sexual route: a mother with an untreated chlamydia infection can pass the bacteria to her baby during vaginal delivery. This can cause eye infections or pneumonia in the newborn. Prenatal screening catches most cases before delivery, which is why testing during pregnancy is standard practice.
Who Is Most at Risk
Sexually active women under 25 have the highest rates of chlamydia infection. This is partly biological (younger cervical tissue is more susceptible) and partly behavioral (higher rates of new or multiple partners in this age group). The CDC recommends annual chlamydia screening for all sexually active women under 25, regardless of symptoms.
For women 25 and older, annual screening is recommended if you have a new sexual partner, more than one partner, or a partner who has other sexual partners or a known STI. Adolescents with higher-risk sexual behavior may benefit from screening more often than once a year.
Reinfection Is Common
Having chlamydia once does not protect you from getting it again. Your immune system does not build lasting resistance to the bacteria, so reinfection happens frequently, especially if a partner wasn’t treated at the same time. This is one of the most overlooked aspects of chlamydia: a woman can be successfully treated, resume sex with the same untreated partner, and become reinfected within weeks.
Both partners need to complete treatment and wait the recommended period before having sex again. Getting retested about three months after treatment helps catch reinfections early, before they cause further damage to the reproductive tract.
How Testing Works
Chlamydia testing is simple. Most tests use a urine sample or a swab of the cervix, vagina, or other potentially infected site. Results typically come back within a few days. Because the infection is so often silent, routine screening is the most reliable way to catch it. Waiting for symptoms means many infections will be missed entirely.
If you’re sexually active and haven’t been tested recently, a screening test is a straightforward way to rule it out or catch it early, when treatment is quick and complications are avoidable.