Yes, chlamydia is a sexually transmitted infection (STI). It spreads through vaginal, anal, and oral sex with an infected partner. The bacterium responsible, Chlamydia trachomatis, can only survive inside human cells, meaning sexual contact is the primary way it passes from person to person. It is one of the most common STIs worldwide and is both preventable and curable with antibiotics.
How Chlamydia Spreads
Chlamydia transmits through direct contact with infected mucous membranes during sex. That includes vaginal intercourse, anal intercourse, and oral sex. You don’t need to have penetrative sex to contract it. Any exchange of genital fluids or direct mucosal contact with an infected area can be enough.
The infection can establish itself in several body sites depending on the type of sexual contact. In women, it most commonly infects the cervix. In men, the urethra is the typical site. Both men and women can also develop rectal chlamydia from receptive anal sex, or from the infection spreading from another site like the vagina. Throat infections are possible too, particularly after giving oral sex to someone with a genital or rectal infection. You can carry the infection in more than one location at the same time.
Chlamydia can also pass from a pregnant woman to her baby during childbirth, potentially causing eye infections or pneumonia in the newborn. Outside of sexual contact and childbirth, casual contact like hugging, sharing food, or using the same toilet does not spread chlamydia. The bacterium cannot survive outside the body for meaningful periods.
Why Most People Don’t Know They Have It
One of the reasons chlamydia spreads so effectively is that most infected people have no symptoms. At least 70% of women and about 50% of men show no signs of infection at the time of diagnosis. This means you or a partner could carry and transmit the bacteria without ever feeling sick.
When symptoms do appear, they typically show up one to three weeks after exposure. Women may notice unusual vaginal discharge, bleeding between periods, or pain during urination. Men often experience a burning sensation when urinating or discharge from the penis. Rectal infections can cause pain, discharge, or bleeding, though many rectal and throat infections produce no symptoms at all.
Because the infection so often flies under the radar, routine screening is the most reliable way to catch it. The CDC recommends annual screening for all sexually active women under 25, and for older women with risk factors like new or multiple sexual partners.
Testing Is Simple and Highly Accurate
The standard test for chlamydia uses a method called nucleic acid amplification, which detects the bacterium’s genetic material. These tests are over 90% sensitive and more than 99% specific, meaning false negatives and false positives are both rare. They catch 20% to 50% more infections than older testing methods.
For women, a vaginal swab is the preferred specimen and performs just as well as a cervical swab collected during a pelvic exam. Self-collected vaginal swabs are an option, making testing more accessible. For men, a urine sample works as well as, and sometimes better than, a urethral swab. If you’ve had oral or anal sex, your provider can test throat and rectal sites with the same type of test.
What Happens If It Goes Untreated
Because chlamydia often causes no symptoms, some people carry the infection for months or even years without treatment. The bacterium has an unusual survival strategy: it can enter a dormant state inside your cells when your immune system mounts a response, then reactivate when conditions improve. This persistence is part of what makes untreated chlamydia so damaging over time.
In women, the most serious consequence is pelvic inflammatory disease, an infection of the uterus, fallopian tubes, or ovaries. PID can cause chronic pelvic pain, scarring of the reproductive tract, and infertility. It also raises the risk of ectopic pregnancy, where a fertilized egg implants outside the uterus. In men, untreated chlamydia can lead to infection of the tube that carries sperm, causing pain and, in rare cases, affecting fertility. For both sexes, having chlamydia increases vulnerability to other STIs, including HIV.
Treatment and Recovery
Chlamydia is cured with a short course of antibiotics. The standard treatment is a seven-day oral regimen. Most people clear the infection completely with this single course. You should avoid sexual contact during treatment to prevent passing the infection to a partner, and any recent sexual partners need to be tested and treated as well, even if they have no symptoms.
Reinfection is common, not because the antibiotics failed but because people are re-exposed to an untreated partner. The CDC recommends getting retested about three months after treatment to catch reinfection early. Having chlamydia once does not give you immunity, so you can get it again any time you’re exposed.
Reducing Your Risk
Consistent and correct use of latex condoms reduces the risk of chlamydia transmission during vaginal, anal, and oral sex. Condoms are not 100% effective because chlamydia can infect areas not covered by a condom, but they significantly lower the odds. Dental dams offer some protection during oral sex.
Beyond barrier methods, reducing the number of sexual partners and choosing partners who have been recently tested both lower your risk. If you’re in a mutually monogamous relationship where both partners have tested negative, the risk drops to essentially zero. Regular screening remains the cornerstone of prevention, especially given how often the infection produces no symptoms at all.