Understanding and Properly Treating Hair Loss Causes

What is Androgenetic Alopecia?

Androgenetic alopecia (AGA), also known as hereditary hair loss, is one of the most common hair conditions worldwide with chronic and progressive progression. Up to 50% of women and 80% of men are affected during their lifetime. In the USA alone, 30 million women and 50 million men suffer from AGA ^[1], while in Switzerland, over 50% of men over 65 are affected. ^[8] In men, hereditary hair loss typically presents as a receding hairline at the temples and hair loss at the crown, while in women AGA usually manifests differently: as even thinning in the crown area with preserved frontal hairline, as a widening part line, or as thinning at the temples. ^[2]

Hair loss mainly occurs on the upper scalp, where the scalp lies over a tighter tissue layer (galea aponeurotica). The affected areas show three typical characteristics: the hair follicles become smaller (miniaturization), more hairs are in the shedding phase, and the growth phase shortens, leading to visible hair loss.

Hair Follicle Miniaturization

The most important feature of AGA is hair follicle miniaturization. The affected hair follicles become smaller with each hair cycle. The hairs become progressively finer and thinner until they barely grow visibly from the scalp. Technically, this is called the transformation from terminal (thick) hairs to vellus hairs (fine hairs).

Miniaturization doesn't occur during hair growth. An affected hair has the same thickness from tip to root. Instead, the shrinking happens during the transition to a new hair cycle: After an old hair has fallen out, a new hair follicle forms. In AGA, this new follicle is smaller than the previous one.

Miniaturization affects not only the follicle itself but also the surrounding tissue. The sheath around the follicle thickens and scar tissue forms. These changes make it difficult for the hair follicles to return to their original size. This is one reason why hair loss progresses.

In affected individuals, the sheaths around the hair follicles are thickened. The fibers can be up to 2.5 times thicker than normal, a sign of beginning scar formation. ^[3] These thickenings take up the space that hair follicles need to grow. Over time, more scar tissue forms, further constricting the follicles and permanently limiting their growth.

More Shedding Than Growing Hairs

Besides miniaturization, AGA also shows an altered ratio between growing and shedding hairs. Each hair goes through a natural cycle: it grows (growth phase), transitions to a resting phase, and finally sheds (shedding phase). After that, a new follicle forms and growth begins anew. A complete cycle normally lasts two to seven years.

In healthy scalps, 80 to 90% of hairs are in the growth phase, 1 to 2% in the transition phase, and 10 to 15% in the shedding phase. This cycle repeats continuously. Hair loss conditions can often be identified by the ratio between growing and shedding hairs.

Normal is a ratio of 1:12 (one shedding hair for every twelve growing hairs). In men with AGA, this ratio can increase to 1:4 (25%), in women even to 2:5 (40%).

Additionally, the growth phase of affected hairs shortens. Instead of growing for several years, they sometimes only grow for months. That's why many affected people notice short hairs at the hairline or crown that never grow longer than a few centimeters.

The Role of Genetics and DHT

AGA is clearly hereditary. Men whose fathers have hair loss carry a 2.5-fold higher risk. ^[4] In affected women too, hair loss often runs in the family. The exact genes haven't been identified yet. Likely several genes play together, which is why inheritance is complex.

Hormones play a central role. Already in the 1940s, it was shown that men without sex hormones (through castration before puberty) never develop hair loss. When affected men are deprived of testosterone, hair loss stops. When given again, it progresses. ^[5]

Thirty years later, scientists identified the crucial hormone: dihydrotestosterone (DHT). DHT is formed from testosterone and is directly responsible for hair loss. Men who cannot form DHT in the scalp don't get hair loss. In bald areas, more DHT is found than in healthy areas. Medications that lower DHT help 80 to 90% of affected men.

DHT is formed when the enzyme 5-alpha-reductase converts testosterone. There are different forms of this enzyme in different tissues (skin, brain, prostate).

In hair loss, mainly type II of this enzyme is involved. In bald areas, it's more active. Men with a gene mutation who cannot form type II enzyme don't get hair loss. Medications like finasteride block exactly this enzyme and therefore help against hair loss.

To work, DHT must bind to androgen receptors on cells. So hair loss requires three things: testosterone, the enzyme 5-alpha-reductase type II, and androgen receptors.

DHT binds 2 to 4 times stronger to these receptors than testosterone and also stays bound longer. ^[6] That's why it has a greater influence on hair follicles. In affected individuals, the follicles react particularly sensitively to DHT, a genetically determined hypersensitivity.

What We Don't Yet Understand

Despite decades of research, many questions remain open: Which genes are exactly involved? Why does DHT increase in some areas? How exactly does DHT lead to miniaturization? Why does DHT promote body hair growth but cause scalp hair loss? Why does hair loss often follow a pattern?

Research is now also investigating other factors like PPAR signaling pathways and retinoid receptors. These insights could lead to more targeted treatments with fewer side effects. ^[7]

Treatment Approaches

Most treatments aim to keep more hairs in the growth phase and stop or reverse miniaturization. Most effective is finasteride for hair loss (Propecia), approved by the US Food and Drug Administration FDA. It inhibits the enzyme that converts testosterone to DHT. Finasteride lowers DHT in the scalp by 50 to 70% and stops hair loss in 80 to 90% of men. After two years, an increase in hair density of about 10% and thickening of the hairs is seen.

In Switzerland, the mediX guidelines for general practitioners recommend individual counseling. Both medications like finasteride in Switzerland and correct minoxidil application as well as other approaches are considered. Modern online treatments enable straightforward access to proven therapies today. Current research is also investigating new approaches: combating inflammation, activating growth signals, or reducing mechanical tension in the scalp. These approaches could lead to more effective treatments with fewer side effects.