Androgenetic alopecia: why hair falls out and how far it goes

Seeing more hair than usual on your pillow, or noticing that the crown is thinning, tends to set off a quiet alarm. The good news is that in the vast majority of cases the cause is the most common form of hair loss there is, and understanding what drives it helps you look at it without panic. Here we explain, calmly and with the figures, why hair falls out in androgenetic alopecia and how far it usually goes.

What it is and what happens to the follicle

Androgenetic alopecia (AGA) is the most common cause of hair loss. It is not that the hair falls out and vanishes all at once: what happens is a progressive miniaturisation of the hair follicle. In other words, follicles that once produced thick hair start to produce hairs that are finer, shorter and less pigmented, until they look like almost imperceptible down and, over time, stop producing visible hair altogether.

One reassuring point is worth underlining: this is a benign and very common dermatological condition. It is not a serious illness and it is not, in itself, a sign of poor health. It is above all a cosmetic matter, and a question of how each person experiences it.

Hormones and genetics: the pairing that explains it

The engine behind this process is hormonal. Testosterone is converted into dihydrotestosterone (DHT) by an enzyme called 5-alpha-reductase. That DHT binds to the androgen receptors in the follicle and shortens the hair's growth phase (the anagen phase), which is precisely what triggers miniaturisation. In the areas where hair thins there is more activity of that enzyme and a greater number of androgen receptors: that is why the loss follows a pattern rather than being uniform.

But hormones do not act alone. A genetic predisposition is also needed. That predisposition is polygenic and inherited, with genes contributed by both parents. The androgen receptor gene sits on the X chromosome, but many other points across the genome are involved, so reducing inheritance to a single side of the family is far too simplistic.

How it is measured and how far it goes

AGA occurs in both men and women, with different patterns, and dermatologists use standard scales to describe how it progresses.

In men

The Hamilton-Norwood scale is used, with stages from I to VII. It describes the typical progression: receding temples and thinning at the crown (the vertex). Prevalence rises with age: in populations of Caucasian origin, roughly half of men show some degree of AGA by the age of 50, and the figure climbs to close to 80% by the age of 70.

In women

The Ludwig scale is used, with grades from I to III. It reflects the characteristic female pattern: diffuse thinning of the central area or the crown, usually preserving the frontal hairline. It is also common and increases with age, particularly after the menopause; it is estimated that around half of women are affected to some degree by later life.

These figures are international estimates and vary depending on the study, the population and the diagnostic method. They are useful for getting a sense of the overall picture, not for putting an exact label on any one person.

Myths worth setting aside

Plenty of explanations for baldness circulate that simply do not stand up. These are three of the most repeated:

• Caps and hats do not cause androgenetic alopecia. There is no evidence that pressure from a piece of clothing causes androgen-driven follicular miniaturisation.
• Washing your hair often or using shampoo does not cause baldness. The hairs you see in the shower are part of the normal physiological shedding of the hair cycle.
• It is not inherited solely 'from your mother's father'. As a polygenic trait, the genetics come from both sides of the family, so looking at only one branch is misleading.

In short, and what to do about it

Androgenetic alopecia combines hormones and genetic predisposition to gradually thin the hair, following recognisable and benign patterns. Understanding it takes the edge off the anxiety, but the degree, the speed and the options depend on each individual case — and the sooner it is assessed, the more follicle there is to preserve.

That is exactly the right order: assess first, decide afterwards. In Spain there is medical treatment for hair loss with a prior assessment, a prescription where appropriate from a registered doctor and ongoing follow-up by the medical team. You can check in a few minutes whether you are eligible.