Testosterone is a steroid hormone. In men, it is synthesized in the testicles and to a lesser extent in the cortex of the adrenal gland. Under its influence, the testicles, prostate and seminal vesicles mature, male-type hair is maintained. In women, the circulating amounts of testosterone are synthesized half by the ovaries and by the cortex of the adrenal gland. Low levels of testosterone are associated with a decrease in libido, and high levels are associated with increased body hair or its combination with other signs of a male body type such as a coarsening of the voice, enlargement of the clitoris, atrophy of the mammary glands, etc.