IN 1999 the American Academy of Paediatrics (AAP) declared that although circumcision carries some health benefits, these do not outweigh the risks of giving a newborn lad the snip. Since then the number of circumcisions in America has fallen from 61% to 56% of baby boys, though it remains well above the global figure of about 30%. In 2007 the AAP set up a task force to update the recommendation. After poring over 1031 peer-reviewed papers, its experts reversed it altogether.

It has been known for a while that circumcision reduces the risk of HIV infection, because the immune cells under the foreskin are vulnerable to the virus. This has led to vastly more circumcisions being performed in AIDS-ridden parts of Africa. The AAP's report revealed that circumcision is also associated with lower rates of infection with the human papillomavirus (HPV), which has been found to collect under the foreskin, and herpes simplex. Since cervical cancer in women is caused by HPV infections, circumcision has some protective effect on men’s female partners too. Nor did the task force find any evidence that circumcision lowers sexual function or pleasure. One study of 5,000 Ugandan men found not only that intercourse was less painful for circumcised men but that, two years after the procedure, they were in fact more sexually satisfied.

These benefits accrue to sexually active adults, not newborns or children, but Colleen Cagno, a paediatrician at the University of Arizona, points out that overall risk of complications is lower when circumcision is performed soon after birth. One reason might be that procedures carried out later on in life tend to involve general anaesthesia, which brings its own risks and which newborns are spared. In any case, circumcisions rarely go wrong in rich countries, where patients can expect proper medical care. In Israel only 0.3% of circumcisions lead to any complications. There is no overall figure for America, but just 0.2% of circumcisions result in "acute" complications.

The report finds that circumcision of newborns benefits them long before they reach sexual maturity. It reduces the risk of urinary tract infections (UTIs) in boys under the age of two. (UTIs are rare among toddlers, but the protection offered may be for life; almost half the male population will suffer from a UTI at least once in life.) The report's authors also reckon that every 909 snips (that is, 0.1% of cases) will lead to one case of penile cancer averted. A cost-benefit analysis recently published in British Medical Journal finds that an average uncircumcised man will incur an additional $450 in health-care costs over a lifetime. This may not sound much, but it is an average; for some individuals the costs may be much greater.

If removing the foreskin brings so many benefits, why was the custom adopted in the first place? Brian Morris, a physiologist at the University of Sydney who together with colleagues reviewed the literature independently and came to the same conclusion as the AAP, thinks that the extra flesh may have played an important role in thwarting infections, acting as "nature's underpants" when man lived in caves. In the modern, hygienic world, such paleolithic protection may be redundant. Or, as in the case of HIV and HPV, positively harmful.

According to the World Health Organisation circumcision is one of the most common medical procedures in the world. The AAP’s recommendations are coming up against millennia-old religious rituals (see article in the print edition). All the more reason that its call for the snip to be carried out only by trained professionals, using painkillers, and with parents' informed consent, deserves attention.