Unprotected oral sex carries the risk of HIV transmission. Oral sex is a form of sexual intercourse in which one partner makes contact with and stimulates his or her partner’s genitals with the oral area. The main modes of HIV transmission include sexual contact, blood transmission, and mother-to-child transmission. The blood, semen, vaginal secretions, and breast milk of HIV-infected people may carry the virus. When open wounds or mucous membranes come into contact with the above substances, infection may result. Due to the thinness of the oral mucosa and the density of capillaries, repeated friction caused by oral sex can easily lead to breakage of the oral mucosa and bleeding, thus infecting through blood transmission. In addition, when there are ulcers and inflammation in the oral cavity of oral sex users, the wound is prone to bleeding, which can lead to HIV infection through blood transmission. Patients who are at risk of HIV infection should seek prompt medical attention and early intervention, which can effectively stop the progression of HIV to avoid delaying the condition.