What is testosterone?

Harris H. McIlwain, MD

The main sex hormone in men is testosterone which is produced by the testes. Not only is testosterone important throughout a man's life cycle, it is a key player even before birth. The testes of a male fetus secrete testosterone which travels through the bloodstream. At this time, testosterone not only makes the genitals grow and function differently than the female anatomy, it also influences the development of the brain and other parts of the body, including the kidney, the liver, and muscle tissue.

During the first years of life, a boy's young body does not produce much testosterone. Then, at puberty, Leydig cells in the testes greatly increase the production of testosterone. At this time, the genitals grow, facial hair begins to grow, the boy’s voice deepens, and more changes occur that mark the transition from childhood to manhood.

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Testosterone is a hormone produced by both men and women, although to a greater extent in men. In men, this hormone is responsible for promoting the development of male sex characteristics, libido, a deep voice, and facial hair. In women, testosterone influences libido, bone density, energy, and hair growth and is needed to produce estrogen.
Testosterone is a male sex hormone, although women have some too. In men, it is made in the testicles. A little bit is also made in the adrenal glands, the small organs that sit on top of the kidneys.

Males make the most testosterone at adolescence. Levels slowly drop as you get older. Unlike women, there is no “male menopause” where testosterone production abruptly declines.

Testosterone does many things. It stimulates your sex drive, energy level, and bone health and helps build muscle mass. Without it, you might have feel depressed, have a lack of trouble concentrating, or a low sex drive. Men need testosterone to be men.

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