What are STIs?

An STI is a sexually transmitted infection. You can get infected during sex without noticing anything at all. Do you have an STI? Then you could pass it on to someone else. Many STIs are easy to treat. But before you can treat an STI you need to know you have one. That is why regular testing is so important!

What kind of infection?

Most STIs are caused by bacteria or a virus. But some are caused by tiny bugs called parasites. 

Bacterial STIs

These STIs are caused by bacteria:

  • chlamydia
  • gonorrhea 
  • syphilis

Viral STIs

These STIs are caused by a virus:

  • genital warts
  • genital herpes
  • hepatitis B
  • HIV


These STIs are caused by a parasite:

  • trichomoniasis
  • pubic lice
  • scabies


If you have an STI, you may experience symptoms like these:

  • Discharge or pus from the vagina, penis or anus (more than usual). The discharge may be watery, milky, yellowish, or greenish and may smell different.
  • A burning sensation, irritation, or pain during or after you pee. Or often needing to pass small amounts of urine.
  • Sores, warts or blisters on the penis, vagina, anus, or mouth.
  • Itching in the pubic hair, or on the labia, anus, or head of the penis.
  • Swollen glands in the groin.
  • Pain in one or both testicles or the epididymis at the back of the testicle.
  • Pain in the lower abdomen.
  • Pain during sex, or irregular or abnormal bleeding after sex or between two periods.

If you have any of these symptoms, it doesn’t necessarily mean you have an STI. The symptom may be caused by something else. To know for certain, get tested.