STIs are infections passed on during sexual contact. STIs are caused by microscopic organisms such as bacteria, viruses or parasites. Examples of STIs include gonorrhoea, syphilis and chlamydia. Most STIs are treatable and curable, so regular STI testing is recommend every 3 to 6 months especially if you have multiple sex partners. Regular testing for STIs is recommended because STIs do not always have symptoms. Not all STIs can be prevented by condom use, but having vaginal or anal sex without a condom can put you at higher risk of getting some STIs. Although oral sex is not considered a risk factor for HIV, some STIs can come from oral sex without a barrier protection such as a condom or dam.