Chlamydia spreads through sexual contact, primarily 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, and in rare cases, from the genitals to the eyes via contaminated hands. It does not spread through casual contact like toilet seats, swimming pools, or sharing towels.
Sexual Transmission: Vaginal, Anal, and Oral
The bacteria that cause chlamydia live in genital secretions, so any sexual activity that involves contact with those fluids creates a route for transmission. Vaginal sex is the most common pathway, but anal and oral sex both carry risk as well. The estimated transmission probability is roughly 4.5% per unprotected sexual encounter, meaning it doesn’t take many exposures for the infection to pass between partners.
Rectal chlamydia is more common than many people realize. It can result from receptive anal sex, but women can also develop a rectal infection without ever having anal sex. In those cases, infected vaginal secretions spread the bacteria to the rectum on their own. This matters because rectal infections rarely cause noticeable symptoms and are almost never tested for outside of specialized clinics.
Oral transmission is less well studied, but chlamydia can infect the throat through oral sex. Throat infections tend to produce few or no symptoms and often clear without anyone knowing they were there, though they can still pass the bacteria to a partner’s genitals during that window.
Why Asymptomatic Carriers Drive Most Spread
The single most important thing to understand about chlamydia transmission is that most people who have it don’t know. About 75% of women and 50% of men with chlamydia have no symptoms at all. That means the majority of transmission happens between people who feel completely fine and have no reason to suspect an infection.
Without symptoms, there’s no trigger to get tested or to pause sexual activity. Someone can carry and transmit chlamydia for weeks or months before it’s ever detected, if it’s detected at all. This is why routine screening matters so much: annual testing is recommended for all sexually active women under 25, and for older women with new or multiple partners. Men who have sex with men and men in high-prevalence settings (like college health clinics or correctional facilities) also benefit from regular screening.
Transmission During Childbirth
A pregnant person with an untreated chlamydia infection can pass the bacteria to their baby as the infant moves through the birth canal. This can cause eye infections (neonatal conjunctivitis) or pneumonia in the newborn, both of which are treatable but potentially serious if missed. This is one reason chlamydia screening is part of standard prenatal care.
Eye Infections From Hand Contact
Chlamydia can infect the eyes when genital secretions are transferred by hand. This is called autoinoculation: you touch infected fluids, then touch your eye, and the bacteria take hold in the conjunctiva. It’s uncommon compared to genital transmission, but it does happen. The resulting eye infection causes redness, discharge, and irritation, and needs treatment to avoid complications. Simple hand washing after sexual contact is the easiest way to prevent it.
How Chlamydia Does Not Spread
Chlamydia requires direct contact with infected body fluids or mucous membranes. The bacteria cannot survive long outside the human body, which rules out a long list of transmission worries. You cannot get chlamydia from toilet seats, swimming pools, hot tubs, shared towels, or doorknobs. Even in the unlikely scenario that infected fluids ended up on a surface, the organisms would need to be present in large enough numbers and would still need a way past intact skin to cause infection. That combination is essentially impossible in everyday life.
Casual contact like hugging, handshaking, sharing food, or sitting next to someone also poses zero risk. Chlamydia is not airborne and does not spread through respiratory droplets.
How Condoms Reduce the Risk
Latex condoms provide a physical barrier against the genital secretions that carry chlamydia. When used consistently and correctly, they significantly reduce transmission risk for chlamydia, along with gonorrhea and several other infections spread through the same fluids. The key phrase is “consistently and correctly,” meaning every time, from start to finish. Inconsistent use dramatically lowers the protective benefit.
Dental dams during oral sex and condoms during anal sex offer the same barrier protection for those routes. Because chlamydia can infect the throat and rectum without obvious symptoms, protection during all types of sexual contact matters, not just vaginal intercourse.
Reinfection After Treatment
Getting treated for chlamydia does not make you immune. You can be reinfected any time you’re exposed again. This is one of the most common patterns: a person gets treated, but their partner doesn’t, and the infection passes right back. Treating both partners at the same time and avoiding sexual contact until treatment is complete (typically seven days) is essential to breaking the cycle. Retesting about three months after treatment is recommended to catch reinfection early.