Chlamydia spreads primarily through vaginal, anal, or oral sex without a condom with someone who has the infection. It can also pass from a pregnant person to their baby during childbirth. Because the infection often produces no symptoms, many people transmit it without knowing they’re infected.
Vaginal and Anal Sex
Vaginal and anal intercourse are the most common routes of transmission. The bacterium that causes chlamydia, called Chlamydia trachomatis, lives in the mucous membranes of the genitals, rectum, and throat. During unprotected sex, the bacteria pass through direct contact with these tissues. Ejaculation does not need to occur for the infection to spread.
Rectal infections deserve special mention. You can get chlamydia in the rectum through receptive anal sex, but the bacteria can also spread from another infected site on your own body, such as the vagina. This means a vaginal infection can lead to a rectal one without anal sex ever taking place.
Oral Sex
Chlamydia can infect the throat through oral sex performed on someone with a genital or rectal infection. The reverse is also possible: a throat infection can spread to a partner’s genitals during oral sex. Throat infections with chlamydia tend to cause fewer problems than genital or rectal infections, but they may increase susceptibility to HIV and can silently pass the bacteria to future partners.
The risk from any single oral sex act is generally lower than from vaginal or anal sex, but it rises with the number of partners and frequency of unprotected contact.
Transmission During Pregnancy and Birth
A pregnant person with an active chlamydia infection can pass the bacteria to their baby as it moves through the birth canal. This can cause eye infections (neonatal conjunctivitis) or pneumonia in the newborn, both of which typically appear in the first weeks of life. Routine prenatal screening catches most cases before delivery, and treatment with antibiotics during pregnancy prevents transmission to the infant.
Eye Infections and Self-Spread
Chlamydia can infect the eyes through a process called autoinoculation. If you touch infected genital secretions and then touch your eye, the bacteria can take hold in the conjunctiva, the thin membrane covering the white of the eye. This form of chlamydial conjunctivitis is directly tied to an existing genital infection.
Lab research published in the journal Cornea found that the bacteria can survive briefly on nonporous plastic surfaces. Under normal room conditions, half of test samples lost viability within about 5 minutes, and complete die-off occurred by 45 minutes. In humid environments, however, viable bacteria persisted for up to 3 hours. This means shared objects like eye instruments or certain surfaces could theoretically carry the infection under the right conditions, though real-world transmission this way is rare.
How It Does Not Spread
Chlamydia does not spread through casual contact. You will not get it from toilet seats, swimming pools, sharing food, hugging, or sitting next to someone. The bacteria cannot survive long on hard surfaces like countertops or door handles. There is a very low theoretical possibility of transmission through contaminated fabrics like sheets or towels, but this is not considered a meaningful route in practice. The infection requires contact with mucous membranes to establish itself.
Why Asymptomatic Cases Matter
The most important thing to understand about chlamydia transmission is that most infected people have no symptoms at all. Roughly 75% of women and 50% of men with chlamydia never develop noticeable signs. Without testing, these individuals can unknowingly pass the infection to every unprotected sexual partner. This silent spread is the main reason chlamydia remains the most commonly reported bacterial sexually transmitted infection in the United States, with millions of new cases each year.
The incubation period, the time between exposure and when symptoms could appear, typically ranges from 7 to 21 days. But since most people remain asymptomatic, waiting for symptoms is not a reliable way to know whether you’ve been infected. Regular screening is the only way to catch and stop the chain of transmission.
How Condoms Reduce Risk
Consistent condom use significantly lowers the chance of getting chlamydia, though it doesn’t eliminate it entirely. A study in the American Journal of Epidemiology found that among people with a known infected partner, using condoms every time reduced chlamydia and gonorrhea rates by about 58% compared to inconsistent or no use. The infection rate dropped from 43% to 30% in that group.
Condoms are most effective when used from start to finish during every sexual encounter, including oral and anal sex. They work by creating a barrier that prevents the bacteria from reaching mucous membranes. The protection isn’t 100% because chlamydia can infect areas a condom doesn’t cover, and because real-world use often involves errors like late application or slippage. Dental dams offer a similar barrier during oral sex. For people at higher risk, annual screening paired with consistent condom use provides the strongest protection against both getting and spreading the infection.