How is HIV transmitted?

Bodily fluids

HIV is transmitted by body fluid to body fluid.  The body fluids that can transmit HIV are:

  • Blood
  • Semen and pre-seminal fluid (pre-cum)
  • Vaginal secretions
  • Breast milk

The body fluids that cannot transmit HIV are:

  • Saliva
  • Urine
  • Tears
  • Sweat
  • Faeces

The virus can be transmitted from one person to another sexually (such as through unprotected sex) or non-sexually (such as through sharing needles).

Sexual Transmission

  • Vaginal Sex
  • Anal Sex
  • Oral Sex

If an infected man has unprotected (no condom) vaginal sex with a woman, he can pass on the virus to her through the lining of the cervix, uterus and womb. If she has any cuts or sores (which may not be visible) then the risk of  transmission is higher as it makes it easier for the virus to get into the bloodstream. If an infected woman has unprotected sex with a man, she can transmit the virus to him through either a sore or cut on his penis, his urethra or the inside of his foreskin.

Anal sex is riskier than vaginal sex, as the membrane (lining) of the anus is thinner and more delicate than the vagina and therefore more prone to tearing. For both vaginal and anal sex, the receptive partner ("the bottom") is at a higher risk of contracting any STI, than the giving partner.

Oral sex is considered very low risk for contracting and transmitting HIV. This is because saliva has enzymes which break down the virus and because the lining of the mouth is tougher than the vagina or anus. There is a hypothetical risk of transmission if sexual fluids come into contact with sores or ulcers in the mouth or if blood from the mouth comes into contact with any genital sores.  This risk is considered extremely small.

The risk of getting the virus through sex is increased if there is any blood present (such as during a woman's period or due to any cuts) or if any partner has another STI or STIs.

Non-Sexual Transmission

  • Sharing needles
  • Mother to child
  • Blood transfusions and products
  • Healthcare workers
  • Tattoos or piercings
  • Needle stick injuries

Sharing needles is a very high risk activity for many blood borne diseases as needles are an efficient way for one person's blood to enter another person's blood stream.

Mothers can transmit many STIs to their newborns either during pregnancy, during delivery or by breastfeeding. There are drugs which can reduce the risk of transmission of these STIs significantly if a mother knows her status early enough in the pregnancy.

It is extremely rare to contract the virus through a blood transfusion carried out in a developed country these days, as all blood donations are routinely screened. However, in countries where blood supplies are not routinely screened, blood transfusion poses a high risk for transmission.