How high is too high for testosterone in female athletes?

South African Olympic gold medalist Caster Semenya has been at the center of controversy over who can compete in women’s events. The International Association of Athletics Federations has ruled she can no longer run in some women’s races unless she lowers her natural levels of testosterone. Now, scientists who study testosterone in female athletes — including such common causes as polycystic ovary syndrome — have weighed in with findings that support the IAAF’s limits. “A policy that responds with sensitivity to those who may have a condition causing high testosterone is needed,” Angelica Lindén Hirschberg of Sweden’s Karolinska Institute said in a statement about her presentation at the European Society of Endocrinology’s annual meeting. “Our recommended limit makes allowances for women with naturally higher levels and mild PCOS, whilst ruling out those with more severe conditions that hugely increase testosterone levels and promote a more male-like physiology."