Chlamydia spreads through sexual contact with an infected person. Vaginal, anal, and oral sex without a condom are the primary routes. It can also pass from a pregnant person to their baby during childbirth, and in rare cases, from infected genital fluids to the eyes through touch. You cannot get chlamydia from toilet seats, swimming pools, or casual contact like hugging or sharing food.
Sexual Contact Is the Primary Route
Chlamydia is caused by a bacterium that infects the mucous membranes of the genitals, rectum, and throat. Any unprotected sexual contact that brings these surfaces together can transmit the infection. That includes vaginal sex, anal sex, and oral sex. You don’t need to have penetrative sex to be at risk. Any direct contact between infected mucous membranes and your own can be enough.
Rectal infections can happen in two ways: through receptive anal sex, or by the bacteria spreading from an existing vaginal infection to the rectum on its own. Throat infections are less common but possible through oral sex with an infected partner.
Most Infected People Have No Symptoms
What makes chlamydia so easily spread is that the majority of people who carry it don’t know they have it. About 75% of women and 50% of men with chlamydia experience no symptoms at all. A person remains contagious from the moment they’re infected until they complete treatment, which means someone can unknowingly pass chlamydia to partners for weeks, months, or even longer.
When symptoms do appear, they typically show up within one to three weeks after exposure, though the incubation period can range from 7 to 21 days. Common signs include unusual discharge, burning during urination, or pain in the lower abdomen. But the absence of symptoms is the norm, not the exception, which is why routine screening matters so much for sexually active people.
How the Bacteria Infects Your Cells
Chlamydia works differently from many other bacterial infections. The bacterium can’t survive long on its own outside the body. Instead, it needs to get inside your cells to live and reproduce. It exists in two forms: a small, tough outer form that can survive briefly outside cells and latch onto new ones, and a larger form that replicates inside cells by hijacking the cell’s own nutrients and energy.
Once the bacterium attaches to the surface of a cell in your genital tract, throat, or rectum, it triggers the cell to pull it inside. There, it creates a protective bubble and begins copying itself. After enough copies are made, the new bacteria either burst out of the cell or pinch off in a packet, ready to infect neighboring cells or be passed to a sexual partner. This cycle is why chlamydia depends so heavily on direct contact between mucosal surfaces. The bacterium simply can’t last long enough on dry, hard surfaces to spread through casual means.
Transmission During Childbirth
A pregnant person with an untreated chlamydia infection can pass the bacteria to their baby during vaginal delivery. As the baby moves through the birth canal, the bacteria can infect the baby’s eyes, causing conjunctivitis, or reach the lungs, potentially leading to pneumonia in the first few months of life. This is one reason prenatal screening for chlamydia is standard practice. Treatment during pregnancy can prevent transmission to the baby.
Eye Infections From Hand Contact
Chlamydia can infect the eyes if infected genital or urinary fluids come into direct contact with the eye’s surface. This typically happens when someone touches infected fluids and then touches their eye. According to the American Academy of Ophthalmology, the transmission route is direct contact between the eye and infected fluids, not airborne exposure or casual proximity. This type of infection is uncommon but serves as a reminder that hand hygiene matters during and after sexual activity.
Ways You Cannot Get Chlamydia
The bacteria that cause chlamydia cannot survive outside the human body for more than a very short time. That rules out a long list of commonly feared transmission routes:
- Toilet seats. The bacteria die quickly on hard surfaces.
- Swimming pools or hot tubs. Chlorinated water and the lack of direct mucosal contact make this essentially impossible.
- Sharing food, drinks, or utensils. Chlamydia does not spread through saliva.
- Hugging, handshakes, or sitting near someone. Casual skin contact is not a risk.
The infection requires contact between mucous membranes or direct exposure to infected bodily fluids. Dry environments and surfaces are hostile to the bacterium.
Reinfection Is Common
Having chlamydia once does not protect you from getting it again. The infection generates little to no lasting immunity. Reinfection rates run between 10% and 20% within 12 months of treatment, largely because people are re-exposed to untreated partners.
A study published in The Journal of Infectious Diseases found that people whose bodies had spontaneously cleared a chlamydia infection on their own (before treatment) had lower reinfection rates than those who needed antibiotics, about 4.5% versus 20%. This suggests that the immune response from fighting off the infection naturally may offer some limited protection, but it’s far from reliable. The practical takeaway: if you’ve been treated for chlamydia, your partners need to be treated too, or you’re likely to get it right back.
Who Is Most at Risk
Chlamydia is the most commonly reported bacterial sexually transmitted infection in the United States. Even with cases declining 8% between 2023 and 2024, more than 2.2 million cases of chlamydia, gonorrhea, and syphilis combined were reported in 2024. The highest rates consistently occur among people ages 15 to 24, partly because of higher rates of new or multiple partners and lower rates of consistent condom use.
Your risk increases with each unprotected sexual encounter with a new partner, especially if that partner hasn’t been recently tested. Since most carriers are asymptomatic, you can’t rely on a partner appearing healthy as any indication of their infection status. Annual screening is recommended for all sexually active women under 25 and for anyone with new or multiple partners.