Hair Follicle Stem Cells: What They Do and Why It Matters
Hair follicle stem cells are the reserve cells that sit in a protected pocket near the top of each follicle and restart the growing phase every time a hair cycle begins again. They are the reason a follicle can produce hair after hair for decades. In pattern hair loss these cells are generally still present, which is an important and often misreported detail.
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Key takeaways
- The reserve cells live in the bulge, a protected region near where the oil gland and the erector muscle meet the follicle.
- They stay dormant most of the time and wake up to start each new anagen, or growing, phase.
- In pattern hair loss the reserve cells usually survive. It is the progenitor cells that do the day to day work which appear to be depleted.
- In scarring alopecias the bulge itself is destroyed, and that loss is permanent. This is why early GP input matters.
- No shampoo, serum or supplement sold in the UK has been shown to switch these cells on, and Watermans makes no such claim.
What are hair follicle stem cells?
Hair follicle stem cells are long lived, slow dividing cells kept in reserve inside each follicle. Their job is not to make hair directly. Their job is to survive, and then at the right moment to produce the fast dividing cells that build a hair fibre. Biologists describe them as quiescent, which simply means resting rather than inactive.
That reserve design is what makes a follicle a renewable organ. A single follicle may cycle around twenty times across a lifetime, growing a hair, resting, shedding it and starting again. Each restart draws on the same protected population, which is why their survival matters far more than their moment to moment activity.
Where are hair follicle stem cells found in the scalp?
The main reservoir sits in a region called the bulge, roughly a third of the way down the follicle, where the arrector pili muscle attaches and just below the oil gland. A second population sits in the gland region itself, and others line the outer sheath of the follicle. The bulge is the one most research concentrates on.
Position explains a great deal about hair loss. The bulge sits above the bulb at the base of the follicle, so processes that damage only the deep part of a follicle leave the reserve intact and hair can return. Inflammation that reaches the bulge, as happens in scarring conditions, takes the reserve with it and nothing comes back.
Why this one fact changes what you should do
If the reserve survives, time and medical options are on your side. If it is destroyed, they are not, and every week of untreated inflammation costs follicles permanently. That is why a sore, scaly, scarred or rapidly changing scalp is a GP appointment rather than a shopping trip.
What do the reserve cells do during the growth cycle?
Each cycle begins when signals from the surrounding tissue wake the resting reserve. Activated cells divide and hand the work to progenitor cells lower down, which build the new fibre through anagen, the growing phase that lasts two to seven years on the scalp. When catagen arrives the lower follicle regresses, and during telogen the reserve returns to rest until the next call.
| Phase | How long on the scalp | What the reserve cells are doing |
|---|---|---|
| Anagen (growing) | 2 to 7 years | Resting again after handing over to progenitor cells |
| Catagen (transition) | About 2 to 3 weeks | Quiet while the lower follicle regresses |
| Telogen (resting) | About 3 months | Dormant, waiting for the signal to restart |
| Exogen (shedding) | Overlaps telogen | Unaffected, the old hair simply releases |
Our fuller walkthrough of the hair growth cycle and its four stages covers the same phases with the timings that matter for shedding. The proportion of your scalp sitting in telogen at any moment, normally about 10 to 15 per cent, is what determines how much you shed day to day.
Do hair follicle stem cells disappear in pattern hair loss?
Research on balding scalp has generally found the bulge reserve still present in numbers similar to non balding scalp, while the progenitor cells that do the building work are markedly reduced. In plain terms the reserve is there but is not being called into action properly, and the follicles shrink rather than vanish. DermNet describes the same process as miniaturisation.
Scarring alopecias behave completely differently. Inflammation destroys the bulge region itself, the follicle is replaced by fibrous tissue, and no future science recovers it. The British Association of Dermatologists is blunt about the consequence, which is that scarring conditions are time critical and need medical attention early rather than a period of watching and waiting.
If you are trying to work out which pattern you have, the three mechanisms behind thinning hair sets them side by side, and the three clue self check gives you something practical to do this week.
Is your problem hair loss, shedding or breakage?
Hair loss, hair shedding and hair breakage involve different parts of the system and only one of them concerns follicle biology at all. Hair loss means the follicle produces less, or nothing, usually through miniaturisation or destruction. Hair shedding means healthy follicles releasing hairs early after a disturbance, with density typically recovering over six to nine months.
Hair breakage happens entirely outside the scalp. The fibre snaps because of heat, tension, colour processing or rough detangling, while the follicle continues working normally. Anyone reading about follicle biology because their hair feels thinner should rule breakage out first, because it is the most common cause and the fastest to change.
| What you see | Which part of the system | How fast it changes |
|---|---|---|
| Wider parting over a year or more | Follicle miniaturising | Slowly, over years |
| Sudden heavy shedding, hairs with bulbs | Cycle disturbance, follicle healthy | Recovers in 6 to 9 months |
| Short blunt hairs and a frizz halo | Fibre damage, follicle healthy | Improves within weeks of changing handling |
| Smooth patches or a shiny, scarred scalp | Possible follicle destruction | Needs a GP appointment now |
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Can anything you buy activate hair follicle stem cells?
No cosmetic product sold in the UK has been shown to wake these reserve cells, and any brand claiming it does is making a medicinal claim it cannot support. The Medicines and Healthcare products Regulatory Agency draws the line clearly: a product that claims to change how an organ in your body works is claiming to be a medicine, with everything that implies.
What cosmetic care can honestly do is smaller and still worthwhile. A gentle wash keeps the scalp surface comfortable. A conditioner reduces the mechanical damage that costs you visible density for no follicular reason. Ingredients such as caffeine, rosemary, niacinamide and hydrolysed lupine protein are used for scalp comfort and fibre condition, not to reprogramme cells.
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Sulphate free, with caffeine, rosemary, biotin and niacinamide. Cleans without stripping and supports a healthy scalp environment for fuller looking hair. A cosmetic shampoo, with no claim on follicle biology.
Condition Me® Hair Growth Conditioner £13.95
Cholesterol, shea butter and hydrolysed lupine protein to reduce breakage during detangling. The most reliable way to keep the density you already have looking like density.
Two ingredient pages worth reading before you buy anything: what niacinamide actually does for hair, and our page on follicular neogenesis, which covers the separate question of whether new follicles can be created at all.
What does the research on hair follicle stem cells actually support?
Three findings are well supported. The bulge holds a durable reserve population. That reserve survives in balding scalp. And its destruction in scarring conditions is permanent. Those three points are consistent across sources and they carry real practical weight for anyone deciding how urgently to act.
Beyond that, caution is warranted. Much of the exciting work uses cultured cells or mouse skin, and mouse hair cycles in synchronised waves while human hair does not, so results translate unevenly. Where good sources disagree, it is usually about whether reduced progenitor activity is a cause of miniaturisation or a consequence of it, and that question is not settled.
What nobody credible claims is that a topical product available today switches the reserve back on. Read any advertisement making that claim as marketing, and check whether the study behind it was done on human scalp or in a dish.
What protects the follicles you already have?
Four habits protect follicle health in ways that are genuinely within your control. Keep tension off the hairline, because traction damage is one of the few causes of permanent loss you can fully prevent. Keep the scalp clean and comfortable, since persistent inflammation is never helpful. Reduce heat. And get bloods checked if shedding increases, because iron, thyroid and vitamin D problems are common and fixable.
None of that is exciting and all of it works. The hair you keep is doing the visual work while anything else plays out, so the cheapest gain available to almost everyone is simply losing fewer hairs to snapping and pulling.
When should you see a GP about hair loss?
See a GP if you have smooth bald patches, a scalp that is sore, red, scaly or shiny, hair coming out in clumps, a parting that has widened noticeably within a year, or shedding alongside tiredness, weight change or irregular periods. Scarring conditions are the urgent group, because the follicle reserve is destroyed while you wait. Ask about ferritin, thyroid function and vitamin D, then make a GP appointment to discuss the results. If your question is about products or a routine rather than a medical one, you can talk to Gail Waterman, our co-founder, as an AI avatar on the Watermans homepage.
Watermans does not run clinics and does not offer consultations. For hair care specifically, the Institute of Trichologists keeps a public register of qualified members in the UK.
What are the most frequently asked questions about follicle biology?
Where exactly are hair follicle stem cells located?
In the bulge, a protected region about a third of the way down the follicle where the arrector pili muscle attaches, just below the oil gland. Further populations sit in the gland region and along the outer sheath.
Are the reserve cells lost in male or female pattern hair loss?
Generally not. Studies of balding scalp find the bulge reserve largely intact while the progenitor cells that build the fibre are reduced, which is why follicles shrink rather than disappear.
Can a serum switch these cells back on?
No cosmetic serum has been shown to do this, and claiming it would be a medicinal claim under UK rules. Watermans products are cosmetic and are sold for scalp comfort and fibre condition.
What destroys the follicle reserve permanently?
Scarring alopecias, where inflammation replaces the bulge with fibrous tissue. Severe burns and some injuries do the same. Once the bulge is gone the follicle cannot restart, which is why early medical input matters.
Does stress affect these cells?
Stress is well established as a trigger for telogen effluvium, which pushes follicles into rest early. That is a cycling effect rather than damage to the reserve, and density usually recovers.
How many times can one follicle cycle?
Around twenty times across a lifetime is the figure usually quoted, with each anagen phase on the scalp running two to seven years. That is why scalp hair can reach a metre and eyebrow hair cannot.
Is stem cell therapy for hair available on the NHS?
No. Cell based hair procedures are not an approved NHS option in the UK. Anything offered privately under that name is worth checking carefully against what has actually been authorised.
If my follicles are still there, why is my hair thinner?
Because a miniaturised follicle makes a finer, shorter fibre each cycle. The count barely changes while the visible volume falls sharply, which is exactly what a widening parting looks like.
What is the bottom line on hair follicle stem cells?
Hair follicle stem cells sit in the bulge, survive in balding scalp, and are destroyed only in scarring conditions, which makes those conditions the genuinely urgent ones. Nothing you can buy switches them on, so read that claim as a warning sign rather than a selling point. Work out whether you are dealing with loss, shedding or breakage, get bloods checked if shedding is worsening, and protect what you have.
The practical purchase, if you make one, is a gentler wash. A sulphate free hair growth shampoo cleans without stripping and cuts the breakage that costs visible density while your follicles carry on doing their job.
Watermans products are 100% cosmetic and do not treat medical hair loss. Individual results may vary.
Sources & references
- NHS, Hair loss (causes and when to see a GP)
- DermNet, Female pattern hair loss (miniaturisation)
- DermNet, Alopecia areata
- British Association of Dermatologists, Alopecia areata leaflet
- Medicines and Healthcare products Regulatory Agency (the line between a cosmetic and a medicine)
- The Institute of Trichologists (register of qualified members)
