Anal sex carries specific health risks for all lovers, be they heterosexual or homosexual. Faeces contain highly infectious matter. The walls of the rectum are only a few cells thick. They are not designed to resist the pressure of a thrusting penis. They tear easily, and microscopic bleeding occurs. If the penis is not washed immediately after anal sex, whatever germs are in the bowel are thrust directly into the vagina. Infected semen, blood, or faeces can then pass directly into the blood system. Repeated attacks of yeast overgrowth can also occur this way.
Whatever the moral stance, hygiene is the top priority. The penis should not touch the vulva, nor should it ever enter the vagina straight from the bowel. Hands, particularly fingernails, are an added danger in anal sex. Wiping with a tissue is not enough. Penis, hands, mechanical toys, all must be thoroughly scrubbed. It is strongly recommended a condom be used during anal sex, and immediately discarded afterwards.