Sexual transmission of HIV

The majority of new HIV infections globally each year are from sexual transmission.

Sexual HIV transmission is well understood. HIV is present in blood, semen and genital fluids. 

Different types of sex carry different risks. For example, giving someone oral sex is usually low risk and receiving oral sex is zero risk. 

Anal or vaginal sex without a condom is a high risk, especially for the receptive partner.

However, there is zero risk if the positive person has an undetecble viral load on treatment, even without condoms. 

The risk of HIV is close to zero if the negative person is using PrEP, even without condoms.

Otherwise, condoms are very effective at stopping HIV, and some other sexually transmitted infections (STIs).

Some STIs, including herpes, gonorrhoea and syphilis, increase the risk of transmitting HIV. 

• Genital fluids are more infectious. 

• An open sore is an easy route of infection. 

• Immune responses to an STI make it easier for HIV to take hold.

Last updated: 1 November 2024.