The brains of children with gender dysphoria react to androstadienone, a musky-smelling steroid produced by men, in a way typical of their biological sex, but after puberty according to their experienced gender, finds a study for the first time. Around puberty, the testes of men start to produce androstadienone, a breakdown product of testosterone. Men release it in their sweat, especially from the armpits. Its only known function is to work like a pheromone: when women smell androstadienone, their mood tends to improve, their blood pressure, heart rate, and breathing go up, and they may become aroused.