EVEN as headline writers have spent recent years bemoaning the supposed demise of sex among the young, the incidence of sexually transmitted disease (STD) has surged in America. Between 2000 and 2016—the latest year for which data are available—rates of chlamydia rose by 98%. Rates of syphilis, which public-health researchers once thought was on the cusp of eradication, have shot up fourfold. Rates for gonorrhoea dropped 24% between 2000 and 2009, but have risen by 48% since then, more than countering the previous fall.

The underlying science of STD transmission is unchanging and uncomplicated: it requires unprotected sex with an infected person. People today, it appears, are simply less worried about the risks. Among heterosexual couplings, this can be partially explained by the increased use of long-term contraceptives, like IUDs, which have reduced the risk of unintended pregnancy. Liberated from their fears of premature spawn, the young and invincible have felt inspired to ditch the rubbers. Unsurprisingly they account for a disproportionate share of new infections. But there has also been trouble for frisky pensioners who, perhaps less concerned with reproduction, have thrown caution to the wind. In the past decade, rates of gonorrhoea for Americans older than 65 have increased by 73%.

Much of the increase in STDs has come from gay and bisexual men. Although a relatively small share of the population, they accounted for 81% of male syphilis cases in 2016, according to the Centres for Disease Control. As with heterosexuals, this seems to be because sex is now seen as less risky. That is due to the advent of PrEP, a prophylactic drug cocktail which gay men can take to nearly inoculate themselves from HIV. The reduced chances of catching HIV—along with the fact that a positive diagnosis is no longer a death sentence—seems to encourage men to drop their guard. A recent study of gay and bisexual men, published in the Lancet, a medical journal, found that as more began taking PrEP, rates of consistent condom usage dropped from 46% to 31%. Recent studies have shown that uptake of PrEP is strongly associated with increased rates of STD infection.

All this shows that changing sexual mores, and a reduced fear of the risks of unprotected sex, seem to be at fault—especially since the problem is not just limited to America. England experienced a 20% increase in syphilis diagnoses in 2017 and a 22% increase in those of gonorrhoea. Other countries in western Europe have seen ever worse outbreaks, sometimes exceeding 50%. Dwindling public spending on STD prevention—which in America has fallen by 40% in real terms since 2003—is not helping matters. Yet the chief methods of prevention, abstinence and condoms, are tried and true. Should these options seem too chaste or chaffing, then prospective partners ought to get an STD test (especially since most infections can be cleared up with a simple course of antibiotics). Verified testing is vital since verbal assurances, especially on the cusp of a liaison, can be misleading.