The main way that HIV is transmitted is through unprotected sex with someone who already has HIV.
Different kinds of sex have different risks attached, anal sex is the most risky, followed by vaginal sex. There is also a risk with oral sex, but the risk is greatly reduced. HIV is present in sexual fluids - semen, pre-ejaculatory fluid, vaginal fluids and anal mucus and this is why it can be passed on during sex. Whether HIV is transmitted is dependent on a number of factors, and these can be quite complex. It is known that viral load is implicated in transmission and the higher the viral load, the higher the risk of transmission.
HIV is also present in blood and there are other ways in which HIV can be transmitted. These are through sharing injecting equipment when taking intravenous drugs, or anything else that can expose someone to someone else’s blood.
HIV can also be passed from a mother to her child through pregnancy, during birth or breast milk. Mother-to-baby transmission in pregnancy is extremely uncommon in the UK, as doctors work with pregnant women to reduce the risk of this happening. Less than 1% of babies born to women living with HIV in the UK are born with HIV themselves.