The major hormone in the male reproductive system is testosterone, often called the "male hormone." This hormone is mainly produced by the testes, and is responsible for developing secondary sex characteristics in males during puberty. These include increased body hair, increased muscle and bone mass, larynx enlargement, increased production from oil and sweat glands, and facial hair. Testosterone also works in a developing fetus to create and grow the penis, scrotum, and prostate. Low levels of testosterone have been linked with dementia and prostate cancer.
The male reproductive system is also influenced by the follicle-stimulating hormones and lutienizing hormones, which cause spermatocytes to go through mitosis and meiosis, allowing spermatozoa to form. A decrease in these two hormones can cause sperm count and health to degrade.