How Hair Follicle Stem Cells Work in the Hair Growth Cycle

Hair follicle stem cells (HFSCs) help renew the follicle through its repeating growth cycle. Many reside in a region called the bulge, where they can remain relatively quiet and become active when the follicle enters a new growth phase. In androgenetic alopecia (AGA), or pattern hair loss, these stem cells may remain present even as the more active progenitor cells needed to build a growing hair become depleted. That distinction helps explain why a follicle can persist but produce progressively finer hair (a review of stem cell-based approaches to hair loss).

The bulge is a reserve for follicle renewal

A hair follicle is a small, living structure in the skin, not simply a strand rooted in place. HFSCs are concentrated in a specialized area of the follicle known as the bulge. These cells can self-renew and, when activated, give rise to descendants that help replenish follicle structures and support hair production. They work in coordination with nearby cells, including dermal papilla cells at the base of the follicle, which help regulate growth signals and the hair cycle (a review of follicle regeneration).

Stem cells and progenitor cells are related but not interchangeable. HFSCs act more like a long-lived reserve; progenitors are their more specialized descendants, which multiply and contribute to active hair production. The follicle depends on communication among these cell populations and their surrounding tissue. A healthy supply of stem cells alone does not guarantee that a follicle will make a thick, visible hair.

What happens during anagen, catagen, and telogen?

The hair cycle has three familiar phases. Anagen is the active growth phase, when follicle cells produce the hair shaft. Catagen is a brief transition in which growth winds down and the lower portion of the follicle regresses. Telogen is a resting phase; the old hair may eventually shed as the follicle prepares for another cycle. The timing and length of these phases vary across follicles, so neighboring hairs are not all in the same phase at once (a review of follicle regeneration and cycling).

Bulge HFSCs generally remain comparatively inactive during much of the cycle, then contribute to renewed growth through signals exchanged with surrounding follicle cells. As a new anagen phase begins, activated stem cells and their progeny help rebuild the growth machinery. This process is not a simple on-off switch: local signals, including those from dermal papilla cells, influence whether and how the follicle enters active growth. Researchers have identified canonical Wnt–beta-catenin signaling as one pathway involved in this regulation (Tosti and colleagues’ review).

Why stem cells can remain in pattern hair loss

In AGA, androgen signaling can disrupt communication between dermal papilla cells and other follicle cells. Dihydrotestosterone (DHT), a hormone made from testosterone, is involved in this process; over time, affected follicles can miniaturize and produce shorter, finer hairs. Research reviewed by Tosti and colleagues describes a pattern in which hair progenitor cells are lost or reduced while HFSCs remain viable. In other words, the follicle’s reserve may still be there, but its ability to generate active growth can be impaired (the review of stem cell-based approaches to hair loss).

This distinction is important, but it should not be mistaken for proof that a dormant follicle can always be restored. The follicle’s surrounding environment and signaling also matter. Current research is investigating cell-based approaches, conditioned media, and other regenerative strategies, but these are not the same as reliably creating a new, fully functioning follicle. A systematic review of human studies in AGA found encouraging signals across several approaches, while also noting small studies, varied protocols, and short follow-up periods (the 2023 systematic review in Cells).

What this means for treatment claims

The phrase “stem cell hair treatment” can refer to different procedures or products, so it is worth asking what cells or materials are used, how they are prepared, and what evidence supports the specific approach. No stem cell or regenerative product is FDA-approved for hair loss. Cell-based methods remain investigational, and there is no established surgery that grows new follicles in a laboratory and transplants them; standard FUE and FUT surgery redistribute a patient’s existing follicles (FDA information on regenerative medicine; ISHRS patient guide).

When you visit a Hair Transplant Clinic, ask the clinician to distinguish established options from experimental or marketed regenerative services. Hair Transplant Clinics may use different descriptions for their offerings, so ask what specifically is being administered and what outcomes have been measured. A careful consultation should also address the cause of hair loss, realistic expectations, and whether a proposed treatment fits your situation—not just the promise of “activating” stem cells.

Frequently Asked Questions

Do hair follicle stem cells make hair grow directly?

They help replenish the follicle, but they do not act alone. Their descendants and surrounding cells, including dermal papilla cells, contribute to the signals and structures needed for active hair production (Tosti and colleagues’ review).

If stem cells remain in a balding follicle, can it be brought back to normal?

Not necessarily. Although HFSCs may remain viable as progenitor cells decline in AGA, impaired signaling and follicle miniaturization also matter. The presence of stem cells alone does not establish that a follicle can be restored to its earlier size or output (the review of stem cell-based approaches to hair loss).

Are stem cell treatments for hair loss proven or approved?

No stem cell or regenerative product is FDA-approved for hair loss, and research approaches should not be presented as established cures. Ask a qualified clinician what the treatment contains, whether it is investigational, and what evidence applies to that exact method (FDA patient information).

Understanding the hair cycle helps separate the biology of follicle renewal from claims made about treatment. If you are concerned about thinning, seek an assessment of the cause and discuss evidence-based options and realistic expectations with a qualified medical professional.