The follicle
A hair follicle is an organ. It has a blood supply, a nerve supply, its own muscle, and a stem cell population that rebuilds it from scratch several times over a lifetime. There are roughly 100,000 on a human scalp and the number you are born with is the number you get.
At the base sits the dermal papilla, a cluster of cells that supplies the growing hair with nutrients and receives the hormonal signals that determine how long it grows. Nearly everything that matters in hair loss happens here rather than in the visible hair, which is dead keratin by the time you can see it.
The visible hair is dead keratin; the organ is below the surface. The dermal papilla at the base is the part every treatment route ultimately addresses — medical routes try to keep it working, a transplant physically moves it, and a scarring alopecia destroys it.
- Cuticle — overlapping scales on the outside; damaged cuticle is why hair feels rough, and has nothing to do with loss.
- Cortex — the bulk of the shaft, carrying its strength and its pigment.
- Medulla — a soft core, present in thicker hairs and often absent in fine ones.
The growth cycle
Follicles do not grow continuously and they do not act together. Each one runs its own cycle, which is why hair thins gradually rather than falling out all at once.
At any moment roughly 87% of follicles are growing, about 1% are in transition, and 10–15% are resting. Losing 50–100 hairs a day is the resting cohort shedding on schedule. What matters clinically is not the number shed but whether the ratio has shifted.
Anagen is the growing phase and it lasts two to seven years. Its length is what determines how long your hair can get: a three-year anagen gives shoulder-length hair, a seven-year anagen reaches the waist. Catagen is a brief transition of two to three weeks. Telogen is a resting phase of around three months, ending in exogen — the shed itself — as a new anagen hair pushes up beneath.
Miniaturisation — what pattern loss actually is
Pattern hair loss is not follicles dying. It is follicles shrinking. With each cycle the anagen phase gets shorter and the follicle produces a slightly finer, shorter, paler hair. Eventually the hair it makes is a barely visible vellus hair, and eventually the cycle stops.
What miniaturisation removes, layer by layer. The cortex — the strength and pigment of the hair — thins first, and the medulla disappears from fine hair entirely. The same follicle is producing both hairs shown; only its output has changed.
This is why treatment is time-sensitive in a way that is genuinely different from most cosmetic decisions. A miniaturised follicle is still a working follicle and can often be helped. Once it has been dormant for years, it cannot. The window is measured in years, but it is a window.
It is also why the first visible sign is usually a change in texture rather than a change in coverage. Hair that has become finer and will not hold a style is the same process, six to eighteen months earlier.
What is normal
Fifty to a hundred hairs a day is normal. Shedding more after a wash is normal, because you are collecting two or three days at once. Seasonal variation is normal — telogen rates rise for most people in late autumn.
What is worth attention: a sustained increase lasting more than three months, a visible change in part width, hair that has become noticeably finer, or shedding accompanied by scalp symptoms such as itching, burning or tenderness.
Common questions
How many hairs a day is too many?
The number is less useful than the trend. Fifty to a hundred is normal, and most people cannot count accurately anyway. A sustained change over three months, or a visible change in part width, is a better signal than any single day.
Does cutting hair make it grow back thicker?
No. Growth happens at the follicle, below the skin. Cutting removes the tapered end, which makes the remaining shaft feel coarser at the tip, but it changes nothing about rate or diameter.
Does wearing hats cause hair loss?
No, unless the hat is tight enough to cause traction over years. Follicles get oxygen from blood supply, not from air.
Why does hair stop growing at a certain length?
Because the anagen phase has a genetically determined length. When it ends the hair stops growing regardless of how it is treated. Length potential is set by cycle duration, not by care.
Can a follicle come back once it has stopped?
A miniaturised follicle that is still cycling can often produce a better hair with treatment. A follicle that has been dormant for years, or destroyed by a scarring process, does not return. This distinction is the single most important one in hair loss.
Is grey hair related to hair loss?
They are separate processes. Greying is pigment cell exhaustion in the follicle; loss is a cycling change. They often arrive around the same age, which is why they get conflated.
References
- Physiology, hair — StatPearls, NCBI Bookshelf
- Hair follicle: function, structure and associated conditions — Cleveland Clinic
What an assessment establishes
- 1.Which process is causing the loss
Pattern loss, telogen effluvium, traction and scarring alopecia look similar in a mirror and behave nothing alike. The examination separates them, because the answer decides which routes are worth discussing at all.
- 2.Whether it is stable or still moving
Loss that is still progressing changes what any treatment can hold. It is the difference between planning around a fixed area and planning around one that will keep widening, and it is judged from history and examination rather than a single photograph.
- 3.Which routes are available to you, and which are not
Donor supply, scalp condition, skin type and how the loss is behaving each rule options in or out. You leave knowing what is on the table and what is not, without a price attached to the conversation.