
Anal sex involves penetration of the anus, usually with a penis, finger, or sex toy. The practice is often considered taboo in certain cultures, so it is unclear exactly how common it is around the world.
Some experts believe that anal sex is becoming more popular among heterosexual couples because pornography has become more accessible, especially on the Internet. Couples who watch anal sex in erotic films may feel curious about trying it.

A December 2018 study in the journal Sexually Transmitted Diseases provides some insights on heterosexual anal sex practices in the United States.
The researchers looked at data from the 2011-2015 National Survey of Family Growth (NSFG), a study of adults aged 18 to 44 living in the United States. Data were available for 11,152 women and 9,218 men.
Overall, 33.2% of women and 37.7% of men had had anal sex at least once in their lives. Among adolescents between the ages of 15 and 19, the rate was 11%.
The study also reported that condom use during heterosexual anal sex was low. Among women who had had anal sex, 20.7% had used a condom the last time they did so. For men, the rate was 30.3%.

For men who have sex with men, the NSFG combines anal and oral sex data. For the 2011-2015 time period, 5.1% percent reported having anal or oral sex with another male in their lifetime. And 3.2% said they had had anal or oral sex with another male during the previous 12 months. (Note: This information comes from the Centers for Disease Control and Prevention. It applies to males between the ages of 15 and 44.)

Risks
The anus does not lubricate like the vagina does. Its lining is also thinner, making it more susceptible to tears.
As a result, anal sex can increase a person’s risk for sexually transmitted infections (STIs) including HPV, HIV, chlamydia, gonorrhea, and genital herpes. Other bacteria and viruses (such as E. coli and hepatitis A) can also be transmitted. In some cases, infections can come from one’s own bowel movements.
Anal sex may also aggravate hemorrhoids and injure the bowel, although these situations are not common.

Tips for Safe Anal Sex
Always use a condom. A new condom should be used for every new sex act. Couples should never use the same condom for vaginal and anal sex. Those who engage in analingus – oral stimulation of the anus – should use dental dams or another type of barrier so that the mouth and tongue are not in direct contact.
Use a lubricant. This can decrease friction in the anus and decrease the risk of tears. Keep in mind that a water soluble (water-based) lubricant should be used with a condom.
Relax beforehand. Being relaxed can make anal penetration more comfortable. Contracting and relaxing muscles of the anus a few times before penetration may help.
Partners who experience severe pain, bleeding, sores, or discharges from the anus should see their doctor as soon as possible.
In cases of painful anal sex or inability to enable anal penetration (anysmus), consulting an expert in sex therapy is recommended.
Resources
Centers for Disease Control and Prevention
“Key Statistics from the National Survey of Family Growth – S Listing”
(Page last reviewed: August 14, 2017)
https://www.cdc.gov/nchs/nsfg/key_statistics/s.htm
Medical News Today
Nall, Rachel, MSN, CRNA
“What are the risks of anal sex?”
(Page last reviewed: August 14, 2017)
https://www.medicalnewstoday.com/articles/324637.php
Sexually Transmitted Diseases
Habel, Melissa A. MPH, et al.
“Heterosexual Anal and Oral Sex in Adolescents and Adults in the United States, 2011–2015”
(Full-text. December 2018)
Sexual Medicine
Benson, Lyndsey S., MD, MS, et al.
“Perceptions of Anal Intercourse Among Heterosexual Women: A Pilot Qualitative Study”
(Full-text. Published online: March 1, 2019)
https://www.smoa.jsexmed.org/article/S2050-1161(19)30002-9/fulltext