Chlamydia spreads primarily through sexual contact, when vaginal fluid or semen carrying the bacteria passes from one person to another. This includes vaginal, anal, and oral sex without a condom. It can also pass from a pregnant person to their baby during childbirth. What makes chlamydia especially easy to spread is that most people who have it don’t know: roughly 75% of women and 50% of men with the infection have no symptoms at all.
Vaginal and Anal Sex
The most common way chlamydia spreads is through vaginal or anal intercourse. The bacteria lives in infected genital fluids, so any unprotected sexual contact that allows those fluids to reach your mucous membranes (the soft tissue lining your genitals, rectum, or throat) creates an opportunity for transmission. Penetration doesn’t have to be involved, and ejaculation doesn’t have to occur. Any exchange of genital fluids can be enough.
Rectal chlamydia infections deserve a separate mention because they can happen in two ways. You can get chlamydia in the rectum through receptive anal sex, but the bacteria can also spread from an existing vaginal infection to the rectum on its own, without anal contact. This means someone could develop a rectal infection without realizing how it got there.
Oral Sex
Chlamydia can spread through oral sex, though it’s generally considered less efficient than vaginal or anal transmission. If you give oral sex to a partner who has a genital or rectal chlamydia infection, the bacteria can infect your throat. The reverse is also true: if you have chlamydia in your throat, you can pass it to a partner’s genitals during oral sex.
Throat infections from chlamydia may cause fewer health complications than genital or rectal infections. However, having chlamydia in the throat can make it easier to pass the infection to others through oral sex, creating a cycle of transmission that’s easy to miss since throat infections rarely cause noticeable symptoms.
Why Asymptomatic Infections Drive Spread
The biggest factor in chlamydia’s spread isn’t any particular sex act. It’s the fact that most infections are invisible. Three out of four women and half of men with chlamydia experience no symptoms whatsoever. That means the majority of cases go undiagnosed and unreported, and infected people continue having sex without knowing they’re passing the bacteria along.
This is why chlamydia remains so common. In 2024, chlamydia was part of more than 2.2 million reported STI cases in the United States (a figure that includes gonorrhea and syphilis). Cases actually declined 8% from 2023, but the true number of infections is certainly higher than what gets reported, precisely because so many people never develop symptoms that would prompt them to get tested.
Because you can’t tell whether a partner has chlamydia by looking at them or even by asking how they feel, regular screening is the most reliable way to catch and stop the chain of transmission.
Mother-to-Child Transmission
A pregnant person with an active chlamydia infection can pass the bacteria to their baby during vaginal delivery. As the baby moves through the birth canal, it comes into contact with infected tissue and fluids. This can lead to eye infections or pneumonia in the newborn. Prenatal chlamydia screening is standard practice for this reason, and treatment with antibiotics before delivery prevents transmission.
Eye Infections and Non-Sexual Spread
Chlamydia can infect the eyes, and this doesn’t always require sexual contact. If infected genital fluids get on your hands and you touch your eyes, the bacteria can cause a painful eye infection called chlamydial conjunctivitis. The same bacteria, in a different form, causes trachoma, a leading infectious cause of blindness worldwide. Trachoma spreads through direct personal contact, shared clothing or bedding, and even flies that carry eye and nose discharge from infected people, particularly young children.
In developed countries, eye infections from chlamydia are more commonly linked to genital-to-eye transfer than to the environmental spread seen with trachoma. But it’s a reminder that the bacteria can travel beyond the genitals when fluids are involved.
Can You Get Chlamydia From Surfaces?
This is one of the most common questions people have, and the answer is reassuring. Chlamydia bacteria can survive on surfaces for only 2 to 3 hours, and only under humid conditions. In practical terms, catching chlamydia from a toilet seat, doorknob, swimming pool, or shared towel is extremely unlikely. The bacteria needs direct contact with mucous membranes and enough viable organisms to establish an infection, conditions that casual surface contact simply doesn’t provide.
You also cannot get chlamydia from hugging, shaking hands, sharing food, or being coughed or sneezed on. It is not an airborne infection. Transmission requires the specific types of intimate or fluid-based contact described above.
How Long You Can Spread It
You can transmit chlamydia for as long as the infection is active in your body, whether or not you have symptoms. Since untreated chlamydia doesn’t resolve on its own, a person who was infected months ago and never got tested could still be spreading the bacteria with every sexual encounter. After starting antibiotic treatment, most guidelines recommend waiting at least seven days before having sex again to ensure the infection is fully cleared and you’re no longer contagious.
Reinfection is also common. Being treated for chlamydia doesn’t give you any immunity. If your partner wasn’t treated at the same time, or if you have a new partner who carries the infection, you can get chlamydia again right away. Getting retested about three months after treatment helps catch reinfections early.