The HIV virus primarily exists in the blood, semen, vaginal secretions, pleural fluid, cerebrospinal fluid, and breast milk of people with AIDS. It is mainly transmitted through sexual contact, including homosexual, heterosexual, and bisexual contact, as well as through blood and blood products. This includes intravenous drug injection, invasive medical procedures, and tattooing. There is also mother-to-child transmission, mainly through the placenta during childbirth and breastfeeding. To prevent AIDS, one must avoid the aforementioned behaviors. Everyday actions such as handshakes, hugs, and social kisses, as well as normal daily contact, do not transmit the HIV virus.