Although oral sex seems to be less risky than anal or vaginal intercourse, there are some factors which may increase the chance of HIV infection. These are:

• Taking semen into the mouth – all the credible reports of oral transmission (except for one) note that ejaculation did occur into the mouth of the individual reported to have been infected
• Bleeding gums, cuts or sores in the mouth
• Inflammation caused by common throat infections, allergies or sexually transmitted diseases such as gonorrhoea.
• The presence of genital piercings or lesions. A study in Sydney (Richters) judged that five gay male seroconverters out of 75 who were interviewed about their sexual behaviour had had oral sex as their only risk factor. Three of the men had had oral sex with men who had a genital piercing. The investigators commented that the possible transmission risk from genital piercings should be investigated.