Once taboo in the Western world, today anal sex has attained the status of a normal sexual practice. This contrasts sharply with recent thinking that viewed anal sex as unnatural and abnormal. In all Abrahamic religions – Christianity, Islam and Judaism, the holy scriptures indirectly or directly forbid anal sex and declare it a sin against God’s design. After religious dogma gave way to liberal thinking and the sexual revolution, many people discovered the appeal of anal sex. What is the physiological basis of this sexual practice? Why does it bring pleasure? As for the active partner in heterosexual couples, many men prefer anal over vaginal sex because the anal sphincter is tighter than the vagina, which brings greater mechanical friction and, accordingly, a more intense sense of pleasure. The physiological basis of sexual pleasure for the receiving partner, on the other hand, is the rich sensory innervation in the rectum. In homosexual men, mechanical stimulation of the prostate is also associated with an intense sensation of pleasure. Also, some sociocultural factors sometimes make anal sex the preferred sexual practice. First of all, it carries no risk of unwanted pregnancy. In some cultures, where breaking the hymen before marriage is considered shameful, anal sex is a “loophole”, a way to get around the ban on premarital sex. But what is the flip side of the coin? What makes anal sex unattractive to many women is that the anus lacks the natural lubrication that vaginal sex has. As a result, anal sex can be uncomfortable and even very painful. We must point out that the lack of lubrication, combined with the small mechanical resistance of the rectal mucosa, makes passive anal sex the riskiest sexual behavior according to the World Health Organization. This is the place to debunk the myths that anal sex doesn’t carry the risk of STDs just because it’s not vaginal. This is a very dangerous fallacy. The truth is diametrically opposite – anal sex carries a much higher risk of sexually transmitted infections. In fact, it carries the highest risk. Apart from all sexually transmitted infections, anal sex combined with vaginal sex also carries a risk of infections that would otherwise not occur. Alternating between vaginal and anal sex necessitates thorough washing of the penis before re-penetration. If a condom is used, which is recommended, it should be changed. Otherwise, bacteria from the vagina can enter the rectum, which should not end up in the rectum because they can inflame it. The condition is called proctitis and is particularly uncomfortable and difficult to treat. Similarly, bacteria from the colon can enter the vagina, which should not be there because they cause vaginitis. If a condom is not used, part of the rectal microflora may enter the penis,which can cause infections and inflammations in this atypical place. NEWS_MORE_BOX The risk of pathogen penetration through the rectal mucosa is much higher than that of vaginal sex for the following reasons. First, the rectal mucosa is much more delicate and resistant to mechanical stress. Second, the high concentration of white blood cells in the mucosa makes it much easier for pathogens to reach the immune system, which is especially risky for HIV infection, which preferentially infects immunocompetent cells. Third, the rectal mucosa is designed to absorb fluids, which also facilitates the penetration of pathogens. Although not of leading importance, the risk of the appearance of anal fissures – tears in the mucous membrane around the anus, rectal prolapse – falling of a part of the rectum or the exacerbation of existing hemorrhoids is still present. Using lubricants greatly reduces the risk of these complications. To summarize in a few words – the use of a condom and lubricant is highly recommended when practicing anal sex. Even if the partner is reliable and free of sexually transmitted infections, the risk of developing proctitis – inflammation of the rectum – or balanitis – inflammation of the head of the penis remains significant if a condom is not worn. Using a lubricant lowers this risk, as well as the risk of painful or uncomfortable mechanical injuries.