Medically reviewed by University of Illinois — Written by Christine Case-Lo on July 7, 2020

Low testosterone prevalence

Low testosterone (low T) affects 4 to 5 million men in the US.

Testosterone is an important hormone in the human body. But it starts to decrease each year after age 30. In some men this can be substantial. Between 19 and 39 percent of older men may have low levels of testosterone.

Older men with low T have increasingly sought testosterone replacement therapy (TRT) in recent years. TRT addresses symptoms such as low libido, poor muscle mass, and low energy.

It’s not just older men that are affected by low T. Young men, even babies and children, can also have this problem.

Symptoms of low T

Low levels of testosterone that are atypical of normal aging are due to other primary or secondary causes of hypogonadism. Hypogonadism in males happens when the testicles don’t produce enough testosterone. Hypogonadism can start during fetal development, during puberty, or during adulthood.

Fetal development

If hypogonadism begins during fetal development, the primary result is impaired growth of external sex organs. Depending on when hypogonadism starts and the level of testosterone present during fetal development, a male child can develop:

  • female genitals
  • ambiguous genitals, neither clearly male or female
  • underdeveloped male genitals

Puberty

Normal growth can be jeopardized if hypogonadism occurs during puberty. Problems occur with:

  • muscle development
  • deepening of the voice
  • lack of body hair
  • underdeveloped genitals
  • overly long limbs
  • enlarged breasts (gynecomastia)