A low testosterone level in men or boys causes hypogonadism. Testosterone is a hormone made by the testicles. Testosterone helps to: Control male features like hair on the face, bigger muscles, and a deep voice Form male genital organs Keep up a man's sex drive Make sperm There are two types of hypogonadism. Problems with the testes, which is primary hypogonadism. Problems with the glands that control how much testosterone is made, which is secondary hypogonadism.