Men and women with hair loss often ask me why their hair is thinning. In most cases hormones are to blame. Dihydrotestosterone (DHT) is the culprit in men, while DHT and other hormones can cause hair loss in women. If you inherit hair follicles that are sensitive to these hormones, the result is a condition called androgenetic alopecia, better known as male pattern baldness and female pattern hair loss. Androgenetic alopecia affects more than 50 million men and 40 million women in the United States, making it the most common cause of hair loss by far.
What is DHT?
DHT is a naturally-occurring by-product of testosterone, the male sex hormone. An enzyme in the hair follicle’s sebaceous (oil) glands helps convert testosterone to DHT. This process happens in both men and women, even though women have less testosterone than men.
How Does DHT Cause Hair Loss?
To understand how DHT causes hair loss, it helps to understand the hair growth cycle. The cycle includes four phases: growing (anagen), transitional (catagen), resting (telogen) and shedding (exogen). DHT builds up in the hair follicles over time, disrupting the growth cycle. In a process called miniaturization, DHT shrinks hair follicles causing strands to reproduce at a slower rate by either shortening the growing phase or lengthening the resting phase. As androgenetic alopecia progresses and DHT continues to adversely affect the follicles, hairs become thinner, more fragile and often lighter in color with each subsequent life cycle. Eventually, the follicles shut down and will no longer produce hair.
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Animation Description: This animation represents a visual interpretation of the production of testosterone and is not indicative of clinical effectiveness.
The hypothalamus releases gonadotropin-releasing hormone (GnRH) in pulses every 60 to 90 minutes to stimulate the pulsatile release of luteinizing hormone (LH) from the pituitary gland into the bloodstream.
LH binds the LH receptor on the Leydig cells of the testes.
Binding initiates a cascade of events which include the conversion of cholesterol (depicted as LDL here) to pregnenolone followed by a series of reactions, which convert pregnenolone to testosterone.
Testosterone, secreted by the testes, diffuses into the peripheral circulation to be carried to target tissues.
In liver, muscle and adipose tissue, testosterone binds directly to its androgen receptor (AR) to exert its biological effect.
In skin, hair, the prostate gland and gonadal tissue, testosterone must be converted to dihydrotestosterone (DHT) by 5-alpha-reductase in order to bind the androgen receptor.
In bone and brain, testosterone is converted by aromatization to estradiol (E2), which binds the estrogen receptor (E2R) to carry out its effects.
There is an accompanying accredited online resource, http://www.ManagingTD.ca that contains the learning materials, as well as videos, animations & an interactive algorithm.
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