Men who have sex with men are vulnerable to HIV, mainly because male-to-male sex has the potential to increase the transmission of HIV. AIDS is a sexually transmitted disease and can be transmitted through sexual contact between heterosexuals. Sexual contact between men of the same sex is likely to come into contact with the rectal mucosa, which is more fragile than the normal skin and vaginal mucosa, and may cause small wounds due to the contact, which can lead to the outflow of one’s own blood, thus coming into contact with body fluids containing HIV, usually semen. Semen is more likely to enter the bloodstream through tiny skin breaks and is more likely to lead to transmission. If a man and a woman have sex with each other in a way that contacts the mucous membrane of the rectum, the probability of transmitting HIV is also slightly higher than that of normal sex between heterosexuals.