Anal sex exposes participants to hazards of two kinds: infections, due to the high number of infectious microorganisms not found elsewhere on the body, and physical damage to the anus and the rectum due to their vulnerability. An insufficient amount of lubricant can make it especially painful or injurious.[17]
Infectious diseases
Among the diseases with which anal sex is associated are HIV,[18] anal cancer,[19] typhoid fever[20] and various diseases associated with the infectious nature of fecal matter or sexual intercourse in general. Among these are: Amoebiasis; Chlamydia; Cryptosporidiosis; Giardiasis; Gonorrhea; Hepatitis A; Hepatitis B; Hepatitis C; Herpes simplex; Human papillomavirus; Lymphogranuloma venereum; Pubic lice; Salmonellosis; Shigella; Syphilis; Tuberculosis.[21][22][23]
HIV/AIDS
The high concentration of white blood cells around the rectum, together with the risk of cuts to the rectum and that one of the functions of the rectum is to absorb fluid, increases the risk of HIV transmission because the HIV retrovirus reproduces within the immune system's T-cells/CD4 cells. Use of condoms and other precautions are a medically recommended way to lessen risk of infections. Unprotected receptive anal sex is the most risky sexual behavior in terms of HIV transmission.[24][25][26]
Physical damage
Physical damage to the rectum and anus can manifest as generalized ano-rectal trauma, hemorrhoids, anal fissures,[21] and rectal prolapse. Damage is more likely if intercourse is forcible or aggressive, if alcohol or other drugs have dulled sensitivity, if communication is poor, or if technique is clumsy.
Incontinence
Incontinence has also been reported; the result of the anal sphincter losing its tonus.[27] A 1993 study published in the Journal of the Royal Society of Medicine found that out of a sample of forty men receiving anal intercourse, fourteen experienced episodes of frequent anal incontinence.[28] Tristan Taormino argues in her book The Ultimate Guide to Anal Sex for Women that proper technique, clear communication, and mutual consent can reduce the risk of incontinence.
Protective measures
As the rectum has no natural lubrication, artificial lubrication is most often required or preferred when penetrating the anus.
Because the vaginal opening is located so close to the anus, without proper precautions it is not uncommon for sexual partners to spread bacteria from the anus into the vagina as well as the urethra, the repercussions of which can include urinary tract infection (UTI), which can lead to infection of the kidneys. This also happens if an object or appendage is inserted rectally and then vaginally before proper cleaning.
Latex gloves or condoms can be used to reduce the risk. It is also possible to take acceptable measures separate from such protection, which include (but are not limited to) hand washing and being conscious and wary of where one's hands and devices are placed.
Condoms may be less effective and more prone to burst or slip during anal sex than vaginal sex. While one study estimates that condoms fail anywhere from 10% - 32% of the time during anal sex,[29] SIECUS indicates a much lower failure rate of 0.5 to 12%.[30]
On this subject, the CDC says "Most of the time, condoms work well. However, condoms are more likely to break during anal sex than during vaginal sex. Thus, even with a condom, anal sex can be very risky. A person should use generous amounts of water-based lubricant in addition to the condom to reduce the chances of the condom breaking."[31]
Some manufacturers offer "extra strong" condoms designed specifically for anal intercourse. These condoms, while stronger, are usually not coated with spermicide and so offer less protection against pregnancy should semen enter a woman's vagina, but will lessen the chance of irritation to the sensitive anus area.
In a 1998 joint conference of the Society for the Scientific Study of Sexuality and the American Association of Sex Educators, Counselors, and Therapists, Jack Morin recommended Kegel exercises for people interested in anal sex to eliminate the possibility of loss of muscle tone, though he claimed he had never observed muscle loosening himself and the comment was primarily concerned with insertion of fists and other large objects.[32]
The danger of anal cancer may be reduced by an HPV vaccine. According to Dr Anne Szarewski, "Men who have sex with men are at a much higher risk than average of anal cancer and genital warts, particularly if they are HIV-positive," and this population may benefit from the vaccine.
