Having unprotected penetrative sex is the most likely way to pass on a sexually transmitted infection (STI).
Hepatitis B is a viral infection that causes inflammation of the liver. It often doesn't cause any obvious symptoms but can lead to a persistent infection. This can eventually cause serious liver disease, including cirrhosis and liver cancer.
Hepatitis B is spread through contact with an infected person's blood or body fluids. Men who have sex with men (MSM) are at risk of hepatitis B but they can be protected by the hepatitis B vaccination.
Vaccination for MSM is available from sexual health clinics, genitourinary medicine (GUM) clinics or from GPs.
Read more about hepatitis B.
Hepatitis C is a viral infection that causes inflammation of the liver. It often doesn't cause any obvious symptoms, but can lead to a persistent infection. This can eventually cause serious liver disease, including cirrhosis and liver cancer.
It is spread through contact with an infected person's blood or body fluids. Men who are concerned they are at risk should consult their doctor or sexual health clinic.
Hepatitis C can be treated and is curable in many cases. Find your local hepatitis C support service.
Read more about hepatitis C.
Gonorrhoea ('the clap')
This bacterial infection can cause stinging when urinating or the feeling that you want to urinate but can't. It's passed on through anal, oral or vaginal sex with an infected person.
Gonorrhoea is treated with antibiotics.
Read more about gonorrhoea.
Non-specific urethritis (NSU)
This is an inflammation of the urethra caused by bacteria. It is also known as non-gonococcal urethritis (NGU) when the condition is not caused by gonorrhoea.
NSU is passed on in the same way as gonorrhoea and often has similar symptoms.
It can also be caused by having lots of sex or masturbating a lot, which can cause the urethra to become inflamed. It can be treated using antibiotics.
Read more about non-specific urethritis.
This is a bacterial infection of the urethra, rectum or throat. There may be a discharge and pain when passing urine, or pain in the testicles (although chlamydia can be symptom-free).
It can be passed on during sex with an infected person in the same way as gonorrhoea and NSU. It's treated with antibiotics.
Read more about chlamydia.
This is a bacterial infection of the intestine that causes severe diarrhoea and stomach cramps. It is often mistaken for food poisoning.
It can be caught during sexual activity, including anal-oral sex ("rimming") and giving oral sex after anal sex. It is spread very easily – all it takes is a tiny amount of infected poo (faeces) getting into your mouth.
A person with shigella can be infectious for up to a month. It can be treated with antibiotics. Men who suspect they have shigella should visit their GP or sexual health clinic to get tested.
Men can avoid getting shigella by washing hands after sex (buttocks, groin and penis too, if you can by taking a shower), and changing condoms between anal and oral sex.
Using latex gloves for fingering or fisting offers protection. And don't share sex toys or douching equipment.
You'll find more information on shigella in this leaflet (PDF, 2.13Mb).
Genital herpes is a viral infection. Symptoms can include painful blisters and ulcers on or around the penis or anus, although some men have no symptoms.
The virus remains in the body and can cause recurrent episodes of blisters.
Genital herpes can be passed on through oral sex with someone with a cold sore around or in their mouth, or by close, skin-to-skin genital contact with someone who has genital herpes.
Antiviral tablets can help the healing process. A GP can prescribe tablets or cream.
Read more about genital herpes.
Syphilis is a bacterial infection that causes a painless ulcer, usually in the genital area. The ulcer will disappear on its own but other symptoms may appear, such as a rash on the body and swollen glands.
In its early stages, syphilis is very infectious and can be passed on by close skin contact during sex. If it's left untreated for years, it can spread to the brain or other parts of the body and cause serious, long-term problems.
Treatment is with antibiotic injections or tablets.
Read more about syphilis.
This is a common viral infection that appears a few weeks or months after sex with an infected person. It can cause pinhead-sized growths, mostly on or around the head of the penis but also in and around the anus.
The sooner warts are treated, the easier they are to deal with. You can't treat genital warts with the same cream you use for warts on the hands. A doctor will freeze them or use a cream to remove them.
Read more about genital warts.
Pubic lice ('crabs')
Public lice (also known as 'crabs') are small, parasitic insects that live in body hair. They are the most common STI .
They only grow to pinhead size so can be difficult to spot, although their tiny dark eggs can be seen stuck to hair.
Pubic lice prefer pubic hair (hair around your testicles and anus) but can also be found in body hair (but not head hair). The lice can also be picked up from clothes, towels and bedding, and symptoms include itching or a rash.
Treatment can be done at home with lotions or creams bought at a chemist (no prescription is needed).
Read more about pubic lice.
This is an infection caused by tiny mites that burrow under the skin. It causes intense itching for most people (though some hardly notice it).
Itching usually starts two or more weeks after sex with an infected person. You can get scabies from sharing beds and towels, but this is less common.
Treatment is similar to treating pubic lice, although you may continue to itch for a few weeks after the mites have been eradicated.
Read more about scabies.
If you have any of the symptoms above or are worried you may have an STI, speak to your GP or visit a genitourinary medicine (GUM) clinic.
Getting tested regularly is a good idea to ensure you have a healthy sex life. NHS services are free.
Find your local sexual health service.
Find your local GUM clinic.