Causes of chlamydia 

Chlamydia is caused by bacteria called Chlamydia trachomatis.

Chlamydia is a sexually transmitted infection (STI), which means that you get it through having unprotected sex (sex without a condom) with someone who has chlamydia.

How you get chlamydia

You can get chlamydia through: 

  • unprotected vaginal sex
  • unprotected anal sex
  • unprotected oral sex
  • your genitals coming into contact with your partner's genitals
  • sharing sex toys when they are not washed or covered with a new condom between each person who uses them

Sexual fluid from the penis or vagina can pass chlamydia from one person to another even if the penis does not enter the vagina, anus or mouth. This means you can get chlamydia from genital contact with someone who has the infection even if there is no penetration, orgasm or ejaculation.

It isn’t clear if chlamydia could be passed on by transferring infected semen or vaginal fluid on the fingers, or by rubbing female genitals together.

Chlamydia cannot be passed on through casual contact, including kissing and hugging, or from sharing baths, towels, swimming pools, toilet seats or cutlery.

Infected semen or vaginal fluid can cause conjunctivitis if it gets into someone’s eye.

Chlamydia and giving birth

During childbirth, a woman with chlamydia can pass the infection on to her baby. If chlamydia develops in the baby there might not be any obvious symptoms at first. Chlamydia in a newborn baby can cause inflammation (swelling) and discharge in the baby’s eyes (known as conjunctivitis) and pneumonia. The midwife or GP can arrange a simple swab test for chlamydia from the baby.

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Condoms and lubricant

If you use lubricant when you have sex with a condom, make sure that it’s water-based (it will say on the label). Oil-based lubricant, such as lotion, baby oil, moisturiser or lipstick, can damage latex condoms.

Page last reviewed: 28/08/2013

Next review due: 28/08/2015