AIDS is caused by the Human Immunodeficiency Virus. This HIV infects the human immune system and makes it unable to fight against infections. Once it enters into body, it destroys CD4+ cells, which are white blood cells that protect the body against various bacteria, viruses and other germs.
The main causes of transmission are unprotected vaginal and anal sex with someone infected with HIV. There is a possibility to get HIV through unprotected oral sex, but the risk is much lower.
Infected mother can also pass on the infection to her child during childbirth, pregnancy, and also through breastfeeding.
Other risk behaviors:
HIV is not passed on through: