Men get chlamydia through vaginal, anal, or oral sex with someone who has the infection. It spreads through direct contact with infected genital, rectal, or throat tissue, and a condom wasn’t used or wasn’t used correctly. The bacteria can’t survive outside the body, so you cannot get chlamydia from toilet seats, towels, swimming pools, or casual contact like hugging or kissing.
How Each Type of Sex Transmits It
Chlamydia passes between people during unprotected vaginal, anal, or oral sex. For men, the most common route is vaginal or anal intercourse with an infected partner. During these acts, the bacteria transfers from infected tissue to the lining of the urethra (the tube you urinate through), where it takes hold and begins multiplying.
Receptive anal sex can lead to a rectal chlamydia infection. Oral sex on an infected partner can cause a throat infection, though this is less common. The infection stays at the site where the bacteria entered, so it’s possible to have chlamydia in your rectum but not your urethra, or vice versa. The bacteria can also spread from one infected site to another on the same person.
What the Bacteria Actually Does
Chlamydia trachomatis is a parasite that can only survive inside human cells. When it contacts the lining of your urethra, rectum, or throat, it latches onto the surface of cells using sugar-like molecules on the cell membrane. It then triggers the cell to pull it inside through a two-step process: first a loose, reversible attachment, then a permanent bond to the cell’s receptors. Once inside, the bacteria hijacks the cell’s resources to reproduce, eventually bursting out and infecting neighboring cells.
This process takes time. After exposure, symptoms typically appear one to three weeks later if they appear at all. A test won’t reliably detect the infection until about one week after exposure, and waiting two weeks catches nearly all cases.
Most Men Have No Symptoms
A major reason chlamydia spreads so effectively is that many men carrying it have no idea. When researchers tested asymptomatic men who had been exposed to an infected partner, roughly 18% tested positive for chlamydia. Among men 24 and younger, that number jumped to nearly 23%. These are men with zero symptoms who would never have known without a test.
When symptoms do show up, they typically include a burning sensation during urination, a watery or cloudy discharge from the penis, or pain and swelling in one or both testicles. Rectal infections may cause pain, discharge, or bleeding, but often produce no symptoms at all. Throat infections are usually silent.
Reinfection From Untreated Partners
Getting treated once doesn’t protect you from getting chlamydia again. One of the most common patterns is the “ping-pong” effect: you get treated, but your partner doesn’t, and the infection passes right back the next time you have sex. The CDC identifies untreated partners as a primary driver of repeat infections.
This is common enough that many states now allow a practice called expedited partner treatment. Your doctor can write a prescription for your partner without seeing them in person, so both of you get treated at the same time. If only one person in a sexual partnership gets antibiotics, reinfection is nearly inevitable once sex resumes.
Who Should Get Tested and How Often
Screening recommendations differ depending on your sexual partners. For men who have sex with women, routine screening isn’t broadly recommended unless you’re in a high-risk setting like an STI clinic, a correctional facility, or you’re under 25 in a community with high chlamydia rates. That said, any new symptoms or a partner’s positive test result are clear reasons to get tested.
For men who have sex with men, the CDC recommends testing at least once a year at every site of sexual contact (urethra and rectum), regardless of whether you use condoms. If you’re on PrEP, living with HIV, or you or your partners have multiple sexual partners, testing every three to six months is recommended. People living with HIV should be screened at their first evaluation and at least annually after that.
Testing itself is straightforward. A urine sample can detect urethral infections. Rectal and throat infections require a swab at those specific sites, so if you only give a urine sample, infections at other locations will be missed. If you’ve had receptive anal or oral sex, let your provider know so the right tests are ordered.
Why Timing Your Test Matters
If you think you were exposed, testing too early can give a false negative. The bacteria needs time to multiply to detectable levels. Most infections show up on a test after one week, and testing at two weeks catches virtually all of them. If you test negative within the first few days of a potential exposure, that result is unreliable and you should retest after the two-week mark.
Chlamydia is curable with antibiotics, and treatment is short. Both you and any recent sexual partners need to complete treatment and avoid sex for at least seven days afterward to prevent passing the infection back and forth. Retesting about three months after treatment is recommended to confirm the infection hasn’t returned.