There are many ways of transmission of AIDS, the most common being blood transmission, sexual contact transmission and vertical transmission from mother to child. The so-called blood transmission refers to the receipt of blood or blood products containing HIV; sexual contact transmission includes both homosexual and heterosexual transmission; and vertical transmission from mother to child refers to the transmission of the virus from the mother to her child when she has AIDS. There are other modes of transmission such as improper tooth extraction, tattooing, sharing of injection needles and occupational exposure of health care workers, and medical transmission, which mainly includes hemodialysis and transplantation of organs containing HIV. Some common ways that are not transmitted are talking, hugging, shaking hands and eating, which are not contagious.