Many people with sexually transmitted infections (STIs) do not get symptoms, so it's worth getting tested even if you feel fine. If you think you have an STI, the earlier you're tested, the sooner treatment can be given if it's needed.
An STI can be passed from one person to another through sexual contact, including vaginal, anal and oral sex.
STIs can pass between men and women, and from women to women and men to men.
Many STIs can be cured with antibiotics. Some, such as HIV, have no cure, but can be treated to prevent them getting worse.
You cannot tell by looking at someone (including yourself) whether they have an infection, so it's important to get a check up if you have had unprotected sex or think you might be at risk.
Many people do not notice symptoms when they have an STI, including most women with chlamydia (external link).
If it's left untreated, chlamydia can affect your ability to get pregnant.
Gonorrhoea (external link) can also affect fertility. Around 50% of women and 10% of men with gonorrhoea do not have symptoms.
Left untreated, STIs can affect your health. If you have any of the symptoms listed below, get tested.
In women and men:
- Pain when you pass urine (pee)
- Itching, burning or tingling around the genitals
- Blisters, sores, spots or lumps around the genitals or anus
- Black powder or tiny white dots in your underwear – this could be droppings or eggs from pubic lice.
- Yellow or green vaginal discharge (external link)
- Discharge that smells
- Bleeding between periods or after sex
- Pain during sex
- Lower abdominal pain
- Discharge from the penis
- Irritation of the urethra (the tube urine comes out of)
These symptoms do not necessarily mean you have an STI, but it's worth seeing a doctor so you can find out what's causing the symptoms and get treatment.
For example, it's possible to get thrush (external link) without having sex, but it can cause STI-like symptoms, such as soreness, itching and discharge.
The majority of HIV infection worldwide has been spread through sexual intercourse. The other main way is through needle-sharing by drug-users and, in the developing world, through childbirth or breastfeeding.
There is a very small number of cases where HIV seems to have been transmitted by oral sex.
Day-to-day living or working with someone with HIV is not a risk to anyone else because the virus is hard to catch, except by intimate contact with bodily fluids.
You can help protect yourself against HIV and other STIs by using a condom correctly every time you have sex.
The condom needs to be put on the penis (or inside the vagina, if it's a female condom) before there is any contact between the genitals.
Find out more on how to use a condom correctly (external link)