Like estrogen and progesterone, testosterone occurs naturally in women and men, although relative levels of these hormones differ by biological sex. Women have about one-tenth the amount of testosterone that men have. Estrogen and progesterone are particularly important for female reproductive functioning. But surprisingly, “testosterone is not necessarily any less important,” says obstetrician and gynecologist Jill Liss, who’s on the faculty at the University of Colorado Anschutz medical school.