How hair grows — and why it stops

A healthy scalp carries roughly a hundred thousand follicles, and each one runs its own independent cycle. In the growth phase — anagen — a hair is produced continuously, for years at a time on the scalp. Then the follicle rests briefly, releases the hair, and starts again. At any moment most of your follicles are growing and a small fraction are resting or shedding, which is why losing fifty to a hundred hairs a day is not loss at all. It is turnover.

Pattern hair loss is what happens when that cycle shrinks. In follicles sensitive to the hormonal signal that drives pattern loss, each successive cycle produces a slightly finer, slightly shorter hair, and the growth phase gets slightly shorter. This is miniaturisation: the follicle does not die — not at first — but the hair it makes becomes progressively less visible, until what it produces is too fine to contribute anything to coverage. The gleam of a thinning crown under light is not absent hair. It is hair that has become too small to see.

This single mechanism explains why every honest treatment works the way it does. Medical treatments that interrupt the hormonal signal slow or stop the shrinking — they protect the cycles you still have. Treatments that support regrowth, including PRP, work on follicles that are miniaturising but alive, coaxing a slightly thicker hair from a struggling cycle. And transplantation works because it side-steps the problem entirely: follicles from the back and sides of the head are not sensitive to the signal, and they remain insensitive wherever they are moved. That is why transplanted hair is permanent, and why the donor zone is the only place a transplant can take from.

Stable means the cycle has stopped shrinking — not that the hair has stopped falling.

It also explains what treatment cannot do. A follicle that has been quiet for many years — in a smooth, bare area — is generally beyond coaxing. This is the fact behind the sentence patients hear from me most often: earlier is better. Medicine protects follicles; nothing yet brings back ones that are gone. The man who comes at the first sign of thinning has options the man who waits a decade does not.

You will often hear us use the word stable. It has a precise meaning here: the cycles have stopped shrinking — loss has plateaued, naturally or with treatment. Stable does not mean the daily shedding has stopped; turnover continues for life. It means the trajectory has flattened, and it matters because a transplant placed into unstable loss will slowly be isolated as the native hair around it continues to miniaturise. Stable first, procedure second — that order is not caution for its own sake. It is how a result still looks right in ten years.

If this sounds more like medicine than the hair-loss industry usually does, that is the point. Thinning hair is a biological process with identifiable causes, and it responds to being treated like one. The assessment is where we work out which part of this story is yours.