Men get chlamydia through sexual contact with an infected partner. The bacteria pass from one person to another during vaginal, anal, or oral sex, entering the body through the thin, moist tissue (mucous membranes) that lines the urethra, rectum, or throat. You don’t need to ejaculate or receive ejaculation to transmit or contract it. In 2024, over 564,000 chlamydia cases were reported in men in the United States alone, making it one of the most common sexually transmitted infections.
How the Bacteria Enter Your Body
Chlamydia is caused by the bacterium Chlamydia trachomatis, which can only live inside human cells. During sex, infectious particles attach to the thin lining of whatever tissue they reach first: typically the urethra (from vaginal or anal sex) or the rectum or throat (from receiving or performing anal or oral sex). Within two hours of contact, the bacteria slip inside your cells and begin multiplying. Over the next 48 to 72 hours, the infected cell fills with new copies of the bacteria, eventually bursting open and releasing them to infect neighboring cells.
This cycle repeats silently. Because the bacteria live inside your cells rather than on surfaces, your immune system is slow to detect and fight the infection, which is why chlamydia can persist for weeks or months without causing noticeable problems.
Specific Routes of Transmission
The most common way men contract chlamydia is through unprotected vaginal sex with an infected partner. The bacteria in vaginal fluid or on cervical tissue come into direct contact with the urethral opening at the tip of the penis, which is enough for infection to take hold. Pre-ejaculate and ejaculate from an infected person can also carry the bacteria, meaning even brief unprotected contact carries risk.
Anal sex, particularly receptive (bottoming), is another high-risk route. Rectal chlamydia infections are especially common among men who have sex with men (MSM), with prevalence in some studies ranging from 2% to 23%. These infections are overwhelmingly asymptomatic, which means they often go undetected. Research from the CDC estimates that roughly 70% of rectal and throat chlamydia infections in MSM would be missed entirely if only urine-based (urogenital) testing were performed.
Oral sex carries a lower but real risk. Chlamydia can infect the throat, though pharyngeal infections appear less common, with prevalence among MSM ranging from 0% to about 3.6% depending on the population studied. Giving oral sex to a partner with a genital or rectal infection is the primary pathway here.
What Does Not Cause Chlamydia
Chlamydia trachomatis lives only in human cells. It cannot survive on surfaces like toilet seats, doorknobs, towels, or clothing. You cannot catch chlamydia from swimming pools, shared food, hugging, or casual contact of any kind. The only transmission route is direct sexual contact with infected tissue or fluids.
Who Faces Higher Risk
Several factors increase your chances of contracting chlamydia. Having multiple sexual partners, concurrent partners (overlapping relationships), or anonymous partners all raise the odds simply by increasing the number of exposures. Condomless sex is the single biggest behavioral risk factor. Substance use before or during sex also correlates with higher infection rates, likely because it reduces the likelihood of using protection.
MSM face disproportionately higher rates for a combination of reasons: the biology of anal sex makes transmission more efficient, sexual networks with higher community prevalence increase exposure, and rectal infections are almost always silent, creating a large reservoir of undiagnosed, transmissible infections. Age matters too. Chlamydia rates are highest among men in their late teens and twenties, partly because of higher rates of partner change and lower rates of routine screening in this group.
Why Half of Men Never Notice
About 50% of men with chlamydia experience no symptoms at all. This is the main reason the infection spreads so effectively. You can carry and transmit it for months without knowing anything is wrong.
When symptoms do appear, they typically start one to several weeks after exposure, though some men don’t notice anything for months. The most common signs in men include a burning sensation when urinating, a clear or cloudy discharge from the penis, and pain or swelling in one or both testicles (though this is less common). Rectal infections, when symptomatic, can cause pain, discharge, or bleeding. Throat infections rarely produce noticeable symptoms.
Testing Timelines That Matter
If you think you’ve been exposed, timing your test correctly makes a real difference in accuracy. A urine test or swab taken at least one week after exposure will catch most infections. Waiting two weeks catches nearly all of them. Testing too early can produce a false negative because the bacteria haven’t multiplied enough to be detected yet.
If you have multiple potential exposure sites, let your provider know. A urine test only checks for urethral infection. Rectal and throat infections require separate swabs of those areas. This is particularly important for MSM, but applies to anyone who has had receptive anal or oral sex.
Reinfection Is Common
Having chlamydia once does not protect you from getting it again. Your body does not build lasting immunity to the bacteria. In one study tracking patients after successful treatment, roughly 17% were reinfected with the same organism within six months, and about 25% contracted some form of STI in that window. This high reinfection rate is driven largely by returning to sex with untreated partners or entering new sexual relationships without protection. If you’re treated for chlamydia, any recent sexual partners need treatment as well, or the infection simply bounces back and forth.