Sexually transmitted infections (STIs) are infections that can be passed on during sex. They are caused by bacteria, viruses or parasites. They are most commonly spread through unprotected vaginal, anal and oral sex, and sharing sex toys.
Skin-to-skin genital contact can also spread some STIs. These include gonorrhoea, syphilis, HPV, herpes, genital warts, pubic lice and chlamydia.