Testosterone is an androgen hormone primarily produced in the testicles of males, although females also produce it in smaller amounts. It plays a crucial role during fetal development in shaping male characteristics, such as the development of male genitalia and the deepening of the voice during puberty. Testosterone is also essential for the maintenance and growth of muscle mass, bone density, and red blood cell production. Testosterone levels gradually decline with age, which can lead to a variety of health issues including decreased muscle and bone mass, increased fat accumulation, and decreased sexual function. Testosterone replacement therapy can help to alleviate some of these symptoms in males with low levels of testosterone.