Hormones form a complex system of signals within the body to trigger human development. They are secreted by glands located in different parts of the body. Testosterone is a major hormone in males and is associated with development of secondary sexual characteristics.
Hormones are chemical signals secreted by a gland to trigger a part of the body to perform a function. The master gland of the body is the pituitary gland. One hormone it secretes, luteinizing hormone (LH), trigger the production of testosterone by the male testes and, to a lesser degree, the female ovaries.
In males, testosterone is involved in development of the secondary sexual characteristics. These characteristics include increased muscle mass, deepening of the voice and body hair growth, including facial hair.
Testosterone levels remain low during childhood. For still uncertain reasons, LH and other hormones kick in and trigger testosterone production. Hair follicles in the face are very receptive of testosterone, producing facial hair as soon as testosterone levels rise.
Because the facial hair follicles are very sensitive, men with low testosterone levels will still produce facial hair. The thickness and coverage of the hair is more dependent on genetic patterns than testosterone levels.
Testosterone and Women
Female ovaries produce testosterone like the testes do, though at lower levels. Testosterone in women is counteracted by Estrogen, another hormone. Estrogen works in balancing calcium levels, muscle mass and breast development in women.