The human immunodeficiency virus causes HIV infections, according to WebMD. Contact with vaginal fluid, blood or semen that is infected can cause someone to contract the virus. Unprotected sex, sharing drug needles, childbirth and breastfeeding are four ways to come into contact with these bodily fluids. Blood transfusions are another way to get HIV, but the risk is tiny, says Mayo Clinic.
To reduce the chances of getting HIV, people should use condoms, including for oral sex, limit themselves to one sex partner at a time, get tested regularly and avoid using mind-altering substances before sex because they can lead to unsafe sex, says WebMD. People should also bypass sharing items such as toothbrushes, razors and syringes. HIV cannot be spread via kissing on the lips or using the same drinking glass because it does not adjust well outside of the body.
HIV also cannot be spread through water, air, insect bites, holding hands, hugging or dancing, says Mayo Clinic. A person can be infected with HIV for years before it becomes AIDS. People are considered to have AIDS when their CD4 white-blood cell count drops below 200 or they contract an AIDS-defining illness such as tuberculosis or pneumocystis pneumonia.