Testosterone is an important hormone. As an androgen, it plays a vital role in the development of male physical characteristics , although it can also be found in lower levels in women. It is involved in a wide range of bodily processes without which the human body would not function properly. Here is a guide to how some of these processes work.
Male sex organs
Development of the male sex organs, including the growth of the penis and testes, begins in the womb and is primarily driven by testosterone levels. Testosterone also causes growth of the prostate gland. The development of male sex characteristics becomes more prominent during puberty. Testosterone is also responsible for continuously producing sperm and controlling sperm levels throughout adult life. As such, a lack of testosterone can cause reduced libido, impotence and even infertility.
Secondary sexual characteristics
In addition to male reproductive organs, testosterone is a key factor in the development of secondary sexual characteristics during puberty. Indeed, too much testosterone can cause puberty to begin early . Secondary sexual characteristics include the growth of the Adam’s Apple and the voice breaking and becoming deeper, as well as increased height and muscle mass (in turn leading to greater physical strength). In contrast, lower testosterone can lead to increased body fat.
Testosterone also has an effect on the sex drive, starting during puberty and continuing throughout adulthood. It increases sexual arousal, with higher levels of testosterone in men being associated with higher levels of sexual activity and more frequent erections. Testosterone can impact the female libido as well.
Facial and body hair
Higher levels of testosterone are associated with more and thicker hair, including facial hair such as beards and moustaches. Hair may also grow in other parts of the body, such as in the armpits and on the chest. Women with higher levels of testosterone may also see increased facial hair growth. Conversely, testosterone can also contribute to baldness and the loss of hair on the scalp in women.
Changing testosterone levels can cause skin issues. This is particularly prominent during puberty, when it can contribute to oily skin and acne.
Increased competitiveness, aggression and confidence are associated with higher levels of testosterone. Testosterone levels can also have an impact on memory, mood and attention span. These changes can become apparent with puberty and continue into adult life. Lack of testosterone can lead to depression and fatigue.
Testosterone can help maintain higher bone density throughout life, which in turn lowers the possibility of developing osteoporosis or fracturing a bone. As testosterone often lowers with age, this is one reason why older people may have lower bone density.
Red blood cell production
Another effect of testosterone is that it indicates to the rest of the body (particularly the bone marrow) when new red blood cells need to be produced. Red blood cells are vital to transport oxygen around the body. They are the most common type of blood cell in humans.
Some medical conditions, including cardiovascular disease and metabolic disease, are associated with lower levels of testosterone. As testosterone levels fall naturally with ageing, these conditions become more common. Research into the relationship between testosterone and heart health is ongoing.
Testosterone works with several other hormones and can, therefore, help control their levels just as they regulate testosterone levels. This includes gonadotropin-releasing hormone, luteinising hormone (LH) and follicle-stimulating hormone (FSH).