FGF Fibroblast Growth Factors in Hair Morphogenesis and G…

FGF: The Architectural Signals Behind Hair Follicle Formation

Fibroblast growth factors (FGFs) are a family of 22 signaling proteins that regulate some of the most fundamental processes in embryonic development, wound healing, and tissue homeostasis. In hair biology, FGFs play critical roles in hair follicle morphogenesis (initial formation), cycling, and regeneration — making them among the most important signaling families you have probably never heard of in the context of hair loss.

FGF Fibroblast Growth Factors in Hair Morphogenesis and Growth

The story begins during embryonic development. Hair follicle formation is initiated by a series of epithelial-mesenchymal interactions: the surface ectoderm (which becomes the epidermis) and the underlying mesenchyme (which becomes the dermis) exchange molecular signals that progressively specify where follicles will form, their type, and their size. FGFs are central mediators of these interactions.

Key FGF Family Members in Hair Biology

FGF7 (Keratinocyte Growth Factor, KGF)

FGF7, also known as KGF, is produced by mesenchymal cells (dermal papilla fibroblasts) and acts on epithelial cells through FGFR2b. It is one of the most potent stimulators of hair follicle epithelial cell proliferation.

A landmark 2000 study by Rosenquist and colleagues demonstrated that FGF7 promotes hair follicle development and that blocking its receptor inhibits follicle formation. In adult follicles, FGF7 helps sustain the anagen phase by supporting keratinocyte proliferation in the hair matrix.

FGF10

FGF10 is closely related to FGF7 and also signals through FGFR2b. During embryonic development, FGF10 is essential for the initiation of hair placode formation — the very first morphological sign that a hair follicle will develop at a given location. Mice lacking FGF10 have significantly fewer hair follicles.

FGF5: The Catagen Promoter

In stark contrast to FGF7 and FGF10, FGF5 actively promotes catagen. Mice with loss-of-function mutations in FGF5 develop the “angora” phenotype — abnormally long hair due to prolonged anagen. This is one of the clearest examples of a single gene controlling anagen duration.

FGF5 is produced by hair follicle outer root sheath cells during late anagen and signals through FGFR1 to initiate the regression program. A 2015 study in the Journal of Investigative Dermatology showed that FGF5 levels increase precisely at the anagen-to-catagen transition in human hair follicles.

FGF2 (Basic FGF)

FGF2 is expressed in dermal papilla cells and supports their survival and function. It also promotes angiogenesis (new blood vessel formation) around the follicle, ensuring adequate nutrient delivery during anagen.

FGF Signaling Mechanism

All FGFs signal through four tyrosine kinase receptors (FGFR1-4) in combination with tissue-specific splice variants. The signaling requires heparan sulfate proteoglycans as co-receptors, which concentrate FGF ligands at the cell surface and promote receptor dimerization and activation.

Upon activation, FGFRs trigger three main downstream pathways:

RAS-MAPK pathway: Promotes cell proliferation — the primary mechanism by which FGF7 and FGF10 stimulate hair matrix growth
PI3K-Akt pathway: Supports cell survival and prevents apoptosis in follicle keratinocytes
PLCγ pathway: Regulates calcium signaling and cell motility, important for follicle morphogenesis

FGF5 Inhibition: A Therapeutic Strategy

Given FGF5’s role as a catagen promoter, inhibiting it has become an attractive therapeutic strategy:

Botanical FGF5 Inhibitors

Several plant-derived compounds have been shown to inhibit FGF5 expression or activity:

Sanguisorba officinalis extract: A Japanese study demonstrated that this botanical extract reduced FGF5 mRNA expression in cultured follicle cells and extended anagen in clinical testing.

Curcuma aeruginosa (pink and white ginger): Research published in 2020 showed that Curcuma extract reduced FGF5 production and promoted hair growth in a mouse model.

These botanical approaches form the basis of several commercial hair care products marketed in Japan and South Korea, where FGF5 inhibition has gained significant consumer awareness.

Anti-FGF5 Antibodies and Peptides

More potent FGF5-blocking strategies are in development. A 2021 study described an anti-FGF5 peptide that extended anagen in human hair follicle organ culture. This approach has the potential for topical formulation and is currently in preclinical development.

FGF7 and FGF10 as Potential Therapies

Topical application of recombinant FGF7 (KGF) has shown promise in promoting hair growth in preclinical models. However, protein-based therapeutics face significant delivery challenges — they are large, unstable, and poorly penetrate the scalp. Liposomal and nanoparticle delivery systems are being explored to overcome these barriers.

Practical Implications

FGF5 is a validated anagen terminator — if your hair has a short anagen phase, excessive FGF5 signaling may be contributing.
Botanical FGF5 inhibitors are available — while not as potent as pharmaceutical approaches, products containing Sanguisorba or Curcuma extracts may modestly extend anagen duration.
FGF7 and FGF10 support growth but are hard to deliver — the science is clear that these growth factors promote follicle activity, but getting them into the follicle in active form remains a challenge.
FGF signaling interacts with other pathways — FGF5 cross-talks with TGF-β and Wnt pathways, meaning that combination approaches may be necessary for optimal results.
Your anagen duration is genetically influenced by FGF5 — genetic variants in FGF5 or its receptor may explain why some people naturally have longer or shorter hair growth phases.

The FGF family illustrates the yin-yang nature of hair follicle signaling: the same family of growth factors that builds the follicle (FGF7, FGF10) also contains the signal that destroys it (FGF5). Understanding and manipulating this balance — promoting anagen-supporting FGFs while inhibiting catagen-promoting FGF5 — represents one of the most promising frontiers in hair loss treatment.

FGF Signaling in Clinical Context

The FGF family’s role in hair biology has several clinical implications that extend beyond direct FGF-targeting therapies. Understanding FGF signaling helps explain the mechanism of several existing treatments and suggests new combination approaches.

Minoxidil, for example, upregulates FGF7 expression in dermal papilla cells, contributing to its hair growth-promoting effects alongside its better-known potassium channel opening and VEGF-inducing activities. This FGF7 upregulation may partially explain why minoxidil is more effective in some patients than others — individuals with intact FGF receptor signaling pathways are better positioned to benefit from the increased FGF7.

FGF5 inhibition has entered the commercial marketplace through Japanese and Korean hair care products containing botanical FGF5 inhibitors. While these products have shown modest results in clinical testing, their efficacy is limited by the relatively weak FGF5-inhibiting activity of the botanical extracts and the challenge of achieving sufficient scalp penetration. Next-generation FGF5 inhibitors — including peptide-based approaches and more potent botanical isolates — could significantly improve on current results.

The interaction between FGF and Wnt signaling is also clinically relevant. FGF signaling promotes Wnt pathway activation in the hair follicle, and the two pathways synergize in promoting anagen. This suggests that combination approaches targeting both FGF activation and Wnt pathway enhancement could be more effective than targeting either pathway alone.

FGF and the Dermal Papilla Expansion Hypothesis

An important concept in hair follicle biology is that the size of the dermal papilla determines the size and quality of the hair fiber produced. Larger dermal papillae produce thicker hairs; smaller papillae produce thinner hairs. FGF7, produced by the dermal papilla, acts on the overlying matrix cells in a paracrine manner, but it also acts in an autocrine manner on the dermal papilla itself through FGFR2-IIIb receptors, promoting papilla cell proliferation and ECM production.

This autocrine FGF7 loop creates a positive feedback mechanism: a larger papilla produces more FGF7, which further promotes papilla growth and ECM production, which supports even more FGF7 production. In androgenetic alopecia, DHT disrupts this positive feedback by reducing FGF7 expression and promoting TGF-β1 production, shifting the balance from papilla expansion to papilla shrinkage. The result is a progressively smaller dermal papilla that produces progressively thinner hairs — the hallmark of follicle miniaturization. Restoring the FGF7 autocrine loop — through exogenous FGF7 delivery, FGFR2-IIIb activation, or DHT blockade — could potentially reverse this miniaturization process by re-expanding the dermal papilla.

FGF7 and the Keratinocyte Stem Cell Niche

FGF7’s role extends beyond the dermal papilla to include direct effects on keratinocyte stem cells in the follicle bulge. These stem cells express FGFR2-IIIb, making them direct targets of FGF7 signaling. During anagen initiation, FGF7 from the dermal papilla activates bulge keratinocyte stem cells, promoting their proliferation and migration to form the new hair germ. A 2020 study demonstrated that FGF7 knockout mice had normal follicle development but impaired anagen re-entry after hair plucking, suggesting that FGF7 is particularly important for stem cell activation rather than initial follicle morphogenesis. This distinction has therapeutic implications: FGF7-based treatments may be most effective for stimulating growth in dormant follicles rather than creating entirely new ones.

FGF Fibroblast Growth Factors in Hair Morphogenesis and Growth