Editor’s Note (May 1, 2019): This article is being republished in light of an international sports court’s decision to bar women with high testosterone levels from competing in certain women’s track events.

Four years ago Indian sprinter Dutee Chand seemed headed for greatness. She became her country's 100-meter champion for women 18 and younger, and the Sports Authority of India called her a “sure shot Olympic medalist.” Yet soon afterward, the Athletics Federation of India banned her from competition because she had an elevated level of the hormone testosterone, the result of a natural condition called hyperandrogenism.

Chand appealed the ruling to the Switzerland-based Court of Arbitration for Sport (CAS), and she won. The decision should allow women with naturally “high T” to compete in all international track competitions. But the International Olympic Committee (IOC), which has banned such female athletes from prior games, has not come out to support the CAS decision. As the Summer Olympic Games in Rio de Janeiro approach, the ambiguity could prevent women with conditions such as Chand's from competing on sports' brightest stage.

This ongoing state of limbo is a mistake. There is no scientific basis for barring these women. Hormone levels akin to Chand's are natural, and there is no evidence that they enhance performance (unlike the doping efforts of the Russian team during the 2014 Sochi Winter Games that were revealed this past spring). Worse, attempts to reduce high testosterone levels below levels specified by the IOC carry serious medical risks for women.

The official Olympic testosterone cutoff for female athletes is 10 nanomoles per liter, but some go beyond it, into the “male” range, and some men fall into the “female” range, thanks to normal hormonal fluctuations that differ from individual to individual. Moreover, high T is not always synonymous with good performance. Some top-level male athletes have testosterone levels that dip into the female range, for example: one recent study of 693 elite athletes in Clinical Endocrinology found that 16.5 percent of males had testosterone levels that were below the male range and almost 2 percent fell in the female range. And almost 14 percent of the women were above the permissible maximum for female athletes.

Things would be different if women were suspected of deliberately taking extra testosterone in the hope—legitimate or not—that it would boost their performance. Even then, existing tests could easily ferret out the subterfuge because naturally occurring testosterone has a different mix of carbon isotopes than an artificially introduced hormone. Tests that detect this artificial signature are already used on suspect male athletes. But if officials determine that a male competitor's unusually high T is natural, the investigation stops. Fairness and science both dictate that women should be treated exactly the same.

Forcing women athletes to bring their natural testosterone down to an “acceptable” level is also potentially dangerous. They would have to take hormone-suppressing drugs or have surgery to remove hormone-producing organs. There is no medical reason for a healthy woman to undergo such treatments, which carry risks of serious side effects, such as an electrolyte imbalance that can cause irregular heartbeats. Other effects include nausea, as well as excessive thirst and urination.

During the Sochi and the 2012 London Olympics, the IOC had invoked its arbitrary standard to ban several women. This year the committee has signaled, in response to questions from Scientific American and other media, that it will not take such action. But the absence of an official statement leaves plenty of uncertainty. Countries could easily continue to disqualify female competitors at preliminary competitions, cutting short their Olympic chances, says Stanford University bioethicist Katrina Karkazis.

Elite athletes are by definition physiological outliers because of their strength, speed and reflexes. Natural hormonal variations, similar to other intrinsic biological qualities—superior oxygen-carrying capacity in the blood, for example—are part of that mix. The IOC should say so explicitly.