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The Biology of hair loss

Male and female pattern hair loss is called androgenetic alopecia (AGA) because both androgens (andro) and genes (genetic) are involved.
Alopecia is the medical term for hair loss. The word alopecia comes from the Ancient Greek word ”αλωπεκια”  which means "without hair".

It is estimated that around 40% of men will suffer from some degree of male pattern baldness by the time they reach the age of 35. This rate continues to increase with age which sees approximately 50% of men over the age of 50 having noticeable hair loss, 65% by the age of 60 and 80% by the age of 80.

Surprisingly, the numbers for women are high, too. Female pattern baldness affects approximately 40% of women by age 50, and management can be challenging.

So, what’s the cause?


biology of hair loss dr bonaros hair loss clinic

Androgenetic alopecia (AGA) is an inherited condition associated with multiple genes. Both dihydrotestosterone -DHT-, and the genes must be present for AGA to occur.

A novel study revealed more than 250 different genetic locations associated with severe hair loss.
It is the most extensive genome-wide study of baldness to date, using data from over 52,000 male participants in the UK Biobank study.  Genes for hair loss make scalp hair follicles extraordinarily sensitive to DHT. This sensitivity eventually causes hair follicles to either stop producing hair or produce only miniaturized “peach fuzz” hair.

DHT is a hormone with powerful androgenic properties, and it derives from testosterone. In humans, testosterone is secreted primarily by the testicles of males and, to a lesser extent, the ovaries of females. On average, in adult males, testosterone levels are about seven to eight times as great as in adult females, but females are much more sensitive to the hormone.

DHT will not cause hair loss to individuals with no genetic predisposition. The genes for AGA must be present, too. The combination of DHT and specific genes will progressively shrink the hair follicles and shorten their life cycle, causing hair to grow out looking thinner and more brittle and fall out faster.

Patterns of inheritance of the AGA genes can sometimes be unpredictable.
Having a father or uncle with AGA makes it probable—but not certain—that AGA will occur in a son or daughter. Especially in women, there may not be any apparent hereditary association. Whereas a man with AGA usually has close male relatives with AGA, no such family pattern may be evident for women.

Hair loss management can be pretty challenging. If you are concerned with hair loss, you should first speak with a hair loss doctor or a trichologist. Hair loss doctors are familiar with the genetics of AGA and can usually counsel a patient regarding the onset and progression of the male or female pattern baldness.

Dr Bonaros is a hair loss doctor servicing patients in Glasgow and all around Scotland. If you are looking into hair restoration solutions, schedule a consultation to get a reliable diagnosis and discuss your treatment options.

Alternatively, please fill out our online assessment form and get advice directly into your inbox.

The article contains excerpts copied from the International Society of Hair Restoration Surgery,, © 2004.