Testosterone is a male hormone (androgen) made by the body. Most of the testosterone in a man's body is produced in the testes.
Just like your cholesterol or blood pressure, there is a numerical range of testosterone levels (also known as T levels) that are considered normal. The brain and the testicles work together to keep testosterone within this range. When levels of testosterone are below normal, the brain signals the testicles to make more. When testosterone levels reach a normal level, the brain signals the testicles to make less.