A Research Review on Hair Follicle Biology and Hair Loss: DHT, Inflammation, Oxidative Stress, Wnt Signalling and Hair Growth
Lustrao Research · Independent Literature Review · August 2026
The Hair Follicle and Hair Loss:
DHT, Inflammation, Oxidative Stress, Vascular Signalling and the Biological Pathways Behind Hair Growth
A detailed review of the biological processes that regulate the hair cycle, follicular miniaturisation and hair growth, from DHT and the androgen receptor to Wnt signalling, stem cells, prostaglandins, inflammation and oxidative stress.
Hair loss is often described in simple terms: DHT attacks the follicle, the follicle shrinks, and the hair becomes thinner. The published literature describes something more complicated.
The hair follicle is a self-renewing mini-organ that repeatedly moves through growth, regression and rest. Its behaviour depends on communication between the dermal papilla, epithelial cells, follicular stem cells, the surrounding tissue and a network of local signalling molecules.
DHT and androgen receptor signalling remain central to androgenetic alopecia. They do not act alone, however. Research has identified downstream changes involving DKK-1, Wnt and beta-catenin, CXXC5, TGF-beta, BMP, IGF-1, VEGF, prostaglandins, inflammatory signalling and oxidative stress. This review examines those pathways and explains how they fit together.
About this review. This article is the web adaptation of Lustrao Research Review 03. It is a narrative synthesis of previously published research. It is not a new clinical trial and it is not itself a peer-reviewed journal publication.
Section 1Abstract
The hair follicle is a self-renewing mini-organ that repeatedly moves through anagen, catagen and telogen. These phases depend on signals exchanged between epithelial cells, the dermal papilla, the surrounding niche, the vasculature and local signalling systems. Hair loss can result when the balance between these signals changes, and androgenetic alopecia is the clearest example of a disorder in which genetically susceptible follicles progressively miniaturise.
DHT and androgen receptor signalling remain central to androgenetic alopecia, but the current literature does not support a model in which DHT acts through a single downstream pathway. Research in human dermal papilla cells and scalp tissue points to changes in TGF-beta, IGF-1, Wnt agonists and antagonists, DKK-1, vascular signalling and prostaglandins. Separate research shows that oxidative stress can accelerate dermal papilla senescence and increase inhibitory factors. Histological studies also report perifollicular inflammation and fibrosis in subsets of patients.
Wnt/beta-catenin is particularly important because it links the dermal papilla and epithelial stem-cell compartments. Its activation is associated with hair-follicle induction and anagen entry, while endogenous antagonists such as DKK-1 and CXXC5 can restrict the pathway. Recent research has connected DHT and PGD2 with CXXC5-mediated suppression of Wnt signalling. Vascular signalling provides another layer. VEGF increases perifollicular vascularisation during anagen, while androgen receptor-mediated paracrine signalling has been shown to promote regression of dermal-papilla microvessels in AGA models.
Taken together, the literature supports a network model of follicular miniaturisation. DHT acts through androgen-sensitive dermal papilla cells, but downstream changes in Wnt signalling, growth factors, prostaglandins, vascular support, inflammatory signalling and cellular stress help determine whether a follicle remains productive or moves toward regression and miniaturisation. This does not mean that every pathway has equal causal evidence in humans. Some of the strongest mechanistic studies come from cultured cells and animal models, and those findings should not be treated as clinical proof.
Section 2Scope and Methodology
This review was conducted as a narrative synthesis of published research identified through targeted searches of PubMed-indexed literature, major biomedical journals and recent review articles. The search concentrated on biological pathways that influence hair-follicle cycling and on mechanisms repeatedly associated with androgenetic alopecia.
Searches combined androgenetic alopecia and hair follicle terms with DHT, androgen receptor, 5-alpha-reductase, dermal papilla, Wnt, beta-catenin, DKK-1, CXXC5, TGF-beta, BMP, IGF-1, VEGF, angiogenesis, prostaglandins, PGD2, PGE2, inflammation, oxidative stress, reactive oxygen species, senescence and hair-follicle stem cells. Reviews were used to identify primary studies, and recent studies published through 2026 were considered where they materially advanced the mechanism under discussion.
Evidence hierarchy. Human clinical or tissue evidence was given priority when available. Human hair-follicle and dermal papilla studies were classified separately from animal and in-vitro experiments. Pathway-level findings are described as mechanistic evidence rather than clinical efficacy.
Important scope limit. This is not a formal PRISMA systematic review. No preregistered protocol, duplicate independent screening team, or meta-analysis was performed. The aim is a traceable, detailed synthesis of the most relevant biological literature rather than a statistical estimate of effect size.
Section 3Hair Follicle Structure and the Hair Cycle
The hair follicle is unusual because it repeatedly rebuilds a hair-producing structure throughout life. The principal phases are anagen, the active growth phase; catagen, the regression phase; and telogen, the resting phase. Exogen describes shedding of the hair shaft and can overlap with telogen. The timing and depth of these phases vary between follicles and body sites.
Hair shedding and follicular miniaturisation are not the same process. Shedding refers to loss of an existing hair shaft, while miniaturisation describes a progressive reduction in follicle size and the diameter and length of the hair it produces. In androgenetic alopecia, the follicle can remain active but produce progressively finer, shorter hairs before the visible density of the scalp changes markedly.
Review of follicle biology and cycling
Human and mammalian hair-follicle biology
Review of follicle structure, the hair-cycle clock and local signalling.
Limitation: Review article rather than a new experimental study; some concepts have since been refined.
Why it matters: Provides the basic framework for interpreting later pathway studies.
Review
Hair-follicle morphogenesis and cycling
Review of WNT, BMP, Shh and other pathways.
Limitation: Review-level synthesis; not a primary clinical study.
Why it matters: Useful map of the major signalling systems examined in this review.
Review
Hair-cycle regulation and factors that shift anagen/telogen balance
Integrative review of inflammation, hormones, stress, nutrition, blood flow and growth factors.
Limitation: Review article and not evidence that any one factor determines hair loss in an individual.
Why it matters: Frames hair loss as a biological network rather than one isolated mechanism.
Section 4The Dermal Papilla and Epithelial-Mesenchymal Signalling
The dermal papilla sits at the base of the follicle and forms part of the mesenchymal signalling compartment. Its interactions with epithelial cells help regulate matrix proliferation, hair-shaft production and the timing of hair-cycle transitions. The evidence consistently treats the dermal papilla as an active signalling centre rather than passive supporting tissue.
Review
Dermal papilla and epithelial signalling
Review of phase-specific epithelial-mesenchymal signals.
Limitation: Review based on diverse experimental models.
Why it matters: Explains why a change in dermal-papilla signalling can alter the behaviour of the rest of the follicle.
Review
Hair-follicle regeneration and stem-cell biology
Review of epithelial-mesenchymal interactions and signalling.
Limitation: Review article.
Why it matters: Provides the framework for later discussion of Wnt, growth factors and stem cells.
Human dermal papilla cell study
Cultured papilla cells from balding and non-balding scalp
Receptor binding measurements in primary dermal papilla cells.
Limitation: Cultured cells may not fully reproduce the native follicle environment.
Why it matters: One reason DHT affects susceptible scalp follicles differently from androgen-insensitive hair follicles.
Human follicle biochemical study
Microdissected human hair-follicle compartments
Measured 5-alpha-reductase activity and androgen metabolites across follicular compartments.
Limitation: Different follicle types have different androgen metabolism; compartment data do not by themselves establish disease causation.
Why it matters: Supports the dermal papilla as a key site for intrafollicular androgen metabolism.
Section 5Androgens, DHT and the Androgen Receptor
Androgenetic alopecia occurs in genetically susceptible follicles and is strongly associated with androgen signalling. DHT is produced from testosterone by 5-alpha-reductase. The androgen receptor is then used by susceptible cells to translate the hormone signal into changes in gene expression and local paracrine signalling.
Human dermal papilla cells
Dermal papilla cells from androgen-dependent and relatively androgen-independent follicles
Compared androgen responses and considered indirect action through dermal papilla signalling.
Limitation: Early mechanistic work and largely cell-based.
Why it matters: Introduces the paracrine model used by later AGA studies.
Human microdissected follicle study
Microdissected hair follicles and cultured dermal papilla/connective tissue sheath cells
RT-PCR localisation of androgen receptor and 5-alpha-reductase isoforms.
Limitation: Culture conditions altered expression, limiting transfer from in-vivo to in-vitro systems.
Why it matters: Shows why follicle context matters when studying androgen metabolism.
Human dermal papilla cell study
Beard and scalp dermal papilla cells
Compared 5-alpha-reductase expression and androgen metabolism.
Limitation: Cell culture study and not a direct AGA outcome study.
Why it matters: Adds evidence that local androgen metabolism differs between follicle types.
Review
Androgen receptor, 5-alpha-reductase and downstream factors
Review of DHT/AR signalling and paracrine factors in AGA.
Limitation: Review rather than new primary data.
Why it matters: Provides a useful synthesis linking androgen signalling to the pathways that follow.
Section 5AWhy DHT Is Central, but Not the Whole Story
DHT is a major upstream signal in androgenetic alopecia, but the available literature does not support a single-step model in which DHT directly shrinks a follicle without intermediate signalling. The androgen receptor is expressed at different levels in different follicle types, and androgen stimulation changes the release of local factors from dermal papilla cells. Those factors include TGF-beta, DKK-1 and Wnt-related regulators, which influence epithelial growth, vascular support and the hair-cycle transition.
Other evidence points to additional processes that can interact with androgen signalling. Oxidative stress can push dermal papilla cells toward senescence and increase inhibitory cytokine or growth-factor signalling. Prostaglandins such as PGD2 can inhibit hair growth, while PGE2 and PGF2alpha show different patterns. Vascular regression in the dermal papilla can reduce local support during miniaturisation. These findings do not replace the androgen model, but they help explain why follicular loss is better described as a network of interacting signals.
Section 6DHT, DKK-1 and Wnt/beta-Catenin
The DHT signal is not the final step. Research in androgen-sensitive dermal papilla cells shows that DHT changes the balance of Wnt agonists and antagonists. DKK-1 is one of the clearest examples of a downstream factor that can inhibit epithelial cell growth.
Human dermal papilla and keratinocyte co-culture
Balding dermal papilla cells and outer-root-sheath keratinocytes
DHT stimulation, DKK-1 measurement and neutralisation experiments.
Limitation: In-vitro model using specific concentrations of DHT.
Why it matters: Provides a direct mechanistic link from androgen stimulation to a follicular growth inhibitor.
Human dermal papilla cells
Androgen-sensitive dermal papilla cells cultured as spheroids and monolayers
DHT stimulation followed by measurement of Wnt5a, Wnt10b and DKK-1.
Limitation: Cell-model evidence.
Why it matters: Links androgen signalling directly with one of the central regenerative pathways in the follicle.
Review
Androgen-Wnt crosstalk in AGA
Review of androgen-induced dermal papilla factors and Wnt signalling.
Limitation: Review-level evidence.
Why it matters: Useful synthesis for the DHT to Wnt connection.
Mouse genetic model
Dermal papilla-specific beta-catenin manipulation
Genetic inactivation of beta-catenin in dermal papilla cells.
Limitation: Mouse genetic model.
Why it matters: Demonstrates that beta-catenin activity in the dermal papilla is required for normal hair regeneration.
Section 7CXXC5 and the Wnt Brake
CXXC5 is a negative regulator of Wnt/beta-catenin signalling. It has gained interest because it is elevated in miniaturised follicles and can interfere with Dishevelled, a component of the Wnt pathway.
Human scalp tissue, human dermal papilla cells and mouse models
Miniaturised human follicles and experimental mouse models
Expression studies, CXXC5 knockout, competing peptide and Wnt activation experiments.
Limitation: Predominantly mechanistic and animal evidence.
Why it matters: Identifies a specific molecular brake on hair-regenerative signalling.
Mouse model and molecular experiments
DHT, PGD2, CXXC5 and Wnt pathway manipulation
DHT and PGD2 experiments combined with CXXC5 knockout and Wnt pathway interventions.
Limitation: Animal and mechanistic study.
Why it matters: Connects three major pathways in this review: DHT, prostaglandins and Wnt signalling.
Section 8Hair Follicle Stem Cells and the Regenerative Niche
Hair follicle stem cells occupy a specialised niche in the bulge and related regions of the follicle. They are periodically activated to produce the progenitor cells that rebuild the matrix and hair shaft. Wnt, BMP, TGF-beta, Notch and Hedgehog pathways all contribute to this regulation.
Review
Hair follicle stem-cell fate and niche biology
Review of Wnt, beta-catenin, BMP and TGF-beta signals.
Limitation: Review and not a clinical study.
Why it matters: Provides the framework for understanding why pathway changes can alter anagen entry.
Review
Wnt/beta-catenin, TGF-beta/BMP, Notch and Hedgehog
Review of hair follicle stem-cell signalling.
Limitation: Review-level evidence and some pathway interactions remain incompletely resolved.
Why it matters: Shows why no single pathway explains hair-follicle regeneration.
Review
Hair follicle stem-cell niche
Review integrating in-vivo tracking and genetic models.
Limitation: Mostly mouse-model evidence.
Why it matters: Establishes the niche as a biological system rather than an isolated cell population.
Review
Age-related stem-cell decline
Review of intrinsic and extrinsic mechanisms in HFSC ageing.
Limitation: Review and age-related biology is broader than AGA alone.
Why it matters: Adds ageing as a biological factor that interacts with androgen and stress pathways.
Mouse stem-cell model
Aged hair-follicle stem cells
Wnt5a and Cdc42 signalling manipulation in aged mice.
Limitation: Animal study.
Why it matters: Shows how ageing can alter the same Wnt network involved in hair regeneration.
Section 9TGF-beta, BMP and Catagen Regulation
TGF-beta and BMP signals do not have a single role. Their effects depend on timing, location and cellular context. In the hair follicle, BMP activity helps maintain quiescence in stem-cell niches, while specific TGF-beta signals can help trigger regeneration. In androgen-sensitive follicles, TGF-beta family signals are also implicated in regression and epithelial growth inhibition.
Human dermal papilla and keratinocyte co-culture
AGA dermal papilla cells
Androgen stimulation and epithelial growth assays.
Limitation: In-vitro mechanism study.
Why it matters: Links androgen signalling in the dermal papilla to a local epithelial growth inhibitor.
Human dermal papilla cells and keratinocytes
AGA coculture model
Further investigation of androgen-inducible TGF-beta1.
Limitation: Early mechanistic study.
Why it matters: Reinforces the DHT and TGF-beta connection.
Human follicle and experimental model
Human hair cycle and catagen-related signalling
TGF-beta2, epithelial proliferation and apoptosis.
Limitation: Mechanistic evidence with a pathway model rather than population-level clinical evidence.
Why it matters: Explains how androgen signalling can contribute to a shortened growth cycle.
Mouse genetic model
BMP pathway in hair follicle stem-cell niche
Conditional BMPR1A ablation.
Limitation: Mouse genetic model.
Why it matters: Shows that increased Wnt activity alone does not reproduce the full hair-building process.
Mouse epithelial stem-cell model
BMP, Noggin, beta-catenin and anagen
Conditional BMP receptor manipulation in epithelial stem cells.
Limitation: Mouse model.
Why it matters: Shows how BMP provides a brake that must be overcome for anagen entry.
Mouse stem-cell model
TGF-beta2, BMP and hair regeneration
Genetic and reporter mouse experiments.
Limitation: Mouse model.
Why it matters: Shows why the same signalling families can have different effects depending on context.
Section 10IGF-1 and Follicular Growth
IGF-1 is one of the growth factors repeatedly discussed in hair biology. Dermal papilla cells produce IGF-1, and reduced IGF-1 signalling has been associated with balding scalp cells and altered follicular growth.
Review and human clinical observations
IGF-1 deficiency, hair growth and dermal papilla signalling
Review of human and experimental evidence.
Limitation: Review and heterogeneous evidence types.
Why it matters: Provides a growth-factor counterpart to the inhibitory pathways discussed above.
Review
IGF-1, PI3K/Akt, MAPK/ERK, VEGF and anagen
Mechanistic review of IGF-1 in hair regeneration.
Limitation: Recent review with therapeutic focus; clinical translation remains limited.
Why it matters: Links IGF-1 to both follicular proliferation and vascular support.
Section 11Vascular Signalling and VEGF
Hair follicles change their vascular requirements as they enter and leave anagen. VEGF is one of the best studied signals connecting hair-follicle cycling with local angiogenesis.
Mouse model
Hair-cycle vascularisation and VEGF
Measured perifollicular vascularisation and manipulated VEGF expression.
Limitation: Mouse model; vascular anatomy differs from humans.
Why it matters: Provides direct experimental evidence that local angiogenesis can influence follicle growth.
Human hair-follicle cell study
VEGF expression in follicular compartments
Measured VEGF mRNA and protein in dermal papilla, follicular keratinocytes and related cells.
Limitation: In-vitro expression study.
Why it matters: Connects VEGF biology from animal models to human follicle tissue.
Human scalp plus mouse mechanistic model
AGA microvascular changes
Transcriptomic analysis and mechanistic experiments on AR and TGF-beta signalling.
Limitation: Mechanistic study combining human tissue and animal experiments.
Why it matters: Provides a pathway linking androgen signalling with loss of local vascular support.
Section 12Prostaglandins and Hair Growth
Prostaglandins are not uniformly stimulatory or inhibitory. The literature distinguishes several prostaglandins, and their relative levels differ between balding and hair-bearing scalp.
Human scalp tissue, human hair follicles and mouse models
Men with AGA and experimental models
Measured PGD2/PTGDS in bald and haired scalp and tested PGD2 effects on hair growth.
Limitation: Translation from experimental pathway to clinical treatment remains unproven.
Why it matters: Strong evidence that PGD2 is a hair-growth inhibitor in AGA biology.
Human scalp biopsies
30 adults with AGA and 30 healthy adults
Two scalp biopsy sites per participant, comparing frontal bald and occipital hair-bearing areas.
Limitation: Biopsy study with a modest sample size.
Why it matters: Shows that several prostaglandin pathways, not PGD2 alone, differ in AGA scalp.
Review
PGD2, PTGDS, GPR44 and AGA
Review of the PGD2 discovery and possible therapeutic targets.
Limitation: Review and not a clinical treatment study.
Why it matters: Provides context for why prostaglandin signalling became an AGA research target.
Section 13Inflammation and Perifollicular Change
AGA has often been described as primarily androgen-driven, but several histological studies have reported perifollicular inflammatory changes. The literature varies in how central these changes are to the disease, and recent work suggests that an inflammatory and fibrotic subset may be clinically relevant, especially in treatment-resistant disease.
Histopathology
Men with AGA at different stages
Histopathological and ultrastructural examination of follicles.
Limitation: Study population and histologic methods limit direct translation to the general AGA population.
Why it matters: Supports the concept of microinflammation and later fibrosis in at least some AGA follicles.
Review
Microinflammation in AGA
Review of inflammatory changes around miniaturising follicles.
Limitation: Older review and not proof of causality.
Why it matters: Shows that inflammation has been considered in AGA biology for more than two decades.
Human scalp histopathology
129 AGA patients from a specialty clinic
Trichoscopy-guided biopsies of balding and clinically non-alopecic scalp, with histology and immunohistochemistry.
Limitation: Referral-centre cohort; this is a selected population and may not represent all AGA.
Why it matters: Suggests an inflammatory endotype of AGA may coexist with androgen-driven pathology in some patients.
Section 14Oxidative Stress and Cellular Senescence
Oxidative stress has been studied both as a local follicular process and as a potential contributor to dermal papilla ageing. The evidence is particularly interesting because oxidative stress can alter cell proliferation, migration and secretion of inhibitory factors.
Human dermal papilla cells
Balding versus non-balding scalp cells
Long-term culture and senescence marker analysis.
Limitation: In-vitro ageing model.
Why it matters: Introduces cellular senescence as a possible component of AGA biology.
Human dermal papilla cells
Patient-matched balding and occipital scalp cells
Exposure to different oxygen conditions and H2O2, with ROS and senescence measurements.
Limitation: In-vitro model and not direct proof of in-vivo causality.
Why it matters: Connects oxidative stress to both cellular ageing and secretion of inhibitory growth factors.
Cell and animal models
Dermal papilla senescence and stem-cell interaction
H2O2-induced senescence in dermal papilla cells plus coculture and in-vivo models.
Limitation: Experimental stress model; not direct evidence that the same sequence occurs in every patient.
Why it matters: Provides a mechanistic link from oxidative stress to impaired follicle regeneration.
Review
NRF2, redox balance and hair-follicle ageing
Review of NRF2 and oxidative-stress biology.
Limitation: Review and preclinical evidence.
Why it matters: Provides a mechanistic rationale for antioxidant pathways in follicle protection.
Human clinical oxidative-stress study
27 patients with AGA and 25 age-matched controls
Blood oxidative-stress parameters measured in patients and controls.
Limitation: Peripheral blood markers do not directly measure events inside the hair follicle.
Why it matters: Adds human clinical evidence for altered systemic oxidative balance, though it is less specific than follicle-cell studies.
Human dermal papilla cells
AGA and matched control follicle cells
Androgen exposure, AR overexpression and knockdown, senescence and DNA-damage markers.
Limitation: In-vitro model.
Why it matters: Provides a direct bridge between androgen receptor signalling, DNA damage and cellular senescence.
Section 15How the Pathways Interact
The studies above describe connected processes rather than unrelated findings. The clearest network begins with androgen signalling in susceptible dermal papilla cells, then branches into several local pathways that affect follicular growth and the timing of regression.
At a glance: how the main pathways connect
| Pathway | Evidence in AGA | Follicular effect | Evidence level |
|---|---|---|---|
| DHT / androgen receptor | Higher AR in balding DPCs; DHT alters downstream factors | Signal that can drive miniaturisation in susceptible follicles | Human cell / tissue + mechanistic |
| DKK-1 | DHT induces DKK-1 in balding DPCs | Restricts epithelial growth and Wnt signalling | Human cell |
| Wnt / beta-catenin | Required for follicular regeneration and stem-cell activation | Promotes anagen and hair-follicle induction | Human cell + animal |
| CXXC5 | Elevated in miniaturised follicles; mediates DHT-PGD2 axis | Suppresses Wnt signalling | Human tissue + animal |
| TGF-beta | Androgen-inducible in balding DPCs; also involved in catagen | Suppresses epithelial growth or drives regression depending on context | Human cell + animal |
| BMP | Restrains stem-cell activation and controls niche thresholds | Maintains quiescence until activation cues overcome the brake | Animal |
| IGF-1 | Lower secretion reported in balding DPCs | Supports proliferation, anagen and vascular signalling | Human cells + review |
| VEGF / angiogenesis | Vascular support rises during anagen; AR signalling can promote DP vessel regression in AGA | Supports follicle size and growth | Human tissue + animal |
| PGD2 / prostaglandins | PGD2 elevated in bald scalp; other PGs differ by region | PGD2 inhibits hair growth; other PGs may have distinct effects | Human scalp + animal |
| Inflammation | Perifollicular inflammatory and fibrotic changes in subsets of AGA | May contribute to treatment resistance and tissue remodelling | Human histology |
| Oxidative stress / senescence | ROS and senescence markers elevated in balding DPCs | Reduced proliferation, migration and hair-inductive capacity | Human cells + animal |
Section 16Emerging Biological Targets
Several mechanisms in this review have already become targets for experimental treatment development. These approaches are important because they show how basic hair-follicle biology is being translated into therapeutic research, but they remain distinct from established clinical treatments.
Review / perspective
Wnt pathway targets including DKK, CXXC5, Axin and GSK-3beta
Evaluation of pathway targets and emerging drug-development approaches.
Limitation: Perspective review; emerging interventions have not all been clinically validated.
Why it matters: Shows the current direction of pathway-specific AGA research.
Review
DKKs, sFRPs and Wnt signalling
Review of endogenous Wnt antagonists influenced by androgen signalling.
Limitation: Recent review with therapeutic emphasis; most proposed interventions remain experimental.
Why it matters: Shows how endogenous Wnt inhibitors are being developed as specific research targets.
Review
Senescence, ageing and AGA
Review of androgen- and ROS-driven senescence in dermal papilla cells and follicular stem cells.
Limitation: Review and mechanistic evidence; clinical translation remains early.
Why it matters: Adds cellular ageing to the network model of AGA.
Recent preclinical research
Dermal papilla senescence, DHT and ROS
Dual pathway experimental nanoparticle therapy targeting DHT and oxidative stress.
Limitation: Preclinical nanoparticle research; not an established human therapy.
Why it matters: Illustrates the current shift toward combination pathway targeting rather than single-mechanism interventions.
Section 17Overall Evidence Summary
- DHT and androgen receptor signalling are central to androgenetic alopecia, especially in genetically susceptible follicles. Human dermal papilla research supports the idea that the local response to androgens is determined partly by receptor and enzyme expression in the follicle itself.
- The dermal papilla is an important signalling centre. It can alter epithelial behaviour through DKK-1, TGF-beta, IGF-1, Wnt-related factors and other paracrine signals.
- Wnt/beta-catenin is a major regenerative pathway. Its activation supports follicular progenitor activity and hair regeneration, while DKK-1 and CXXC5 act as inhibitory influences in experimental AGA models.
- Hair follicle stem cells are controlled by a niche in which Wnt, BMP, TGF-beta, Notch and other signals interact. A change in one pathway can alter the response of the others.
- TGF-beta and BMP have context-dependent effects. BMP often restrains stem-cell activation, while specific TGF-beta signals can either help initiate regeneration or contribute to catagen and epithelial suppression depending on location and timing.
- IGF-1 and VEGF are associated with active growth. IGF-1 supports proliferation and anagen biology, while VEGF is strongly linked to perifollicular angiogenesis and follicle size in experimental models.
- Prostaglandins provide another layer of regulation. PGD2 is elevated in bald scalp and inhibits growth, while other prostaglandins show different patterns and cannot be treated as interchangeable.
- Inflammation and oxidative stress appear to contribute to AGA biology in at least some patients and experimental systems. Perifollicular inflammation and fibrosis are particularly relevant in advanced or treatment-resistant disease, while oxidative stress is linked to dermal papilla senescence and increased inhibitory signalling.
- The overall model is therefore network-based. DHT is a major upstream driver, but its effects are translated through local changes in growth factors, Wnt signalling, prostaglandins, vascular support, inflammatory signalling and cellular stress.
Section 18Limitations
- This is a narrative literature review, not a formal systematic review or meta-analysis.
- Much of the mechanistic evidence comes from cultured cells and animal models. These models are useful for testing pathways but cannot establish the same effect in humans.
- AGA is genetically heterogeneous and the molecular response to androgens differs between follicle types and scalp regions.
- Inflammation, oxidative stress and vascular changes may be important in subsets of patients, but the literature does not support treating any one of these as the single cause of AGA.
- Pathway studies often use concentrations or experimental interventions that do not correspond directly to commercial topical products.
- Wnt, BMP and TGF-beta signalling can have different effects depending on the timing, cell type and tissue compartment studied.
- Evidence that an experimental pathway can be manipulated to induce hair growth does not establish that the pathway can be safely or effectively targeted in routine clinical care.
- The review does not attempt to determine the efficacy of any particular finished commercial formulation.
- DHT and androgen receptor signalling are central to androgenetic alopecia in genetically susceptible follicles.
- The dermal papilla is a major signalling centre, linking androgen signalling to epithelial behaviour and growth-factor pathways.
- Wnt and beta-catenin support follicular regeneration, while DKK-1 and CXXC5 can act as inhibitory influences in experimental models.
- Hair-follicle stem cells depend on a changing niche involving Wnt, BMP, TGF-beta, Notch and related signals.
- IGF-1 and VEGF are associated with active growth, while prostaglandins can have different effects depending on the molecule.
- Inflammation and oxidative stress appear to contribute in some settings, but neither is supported as the single cause of AGA.
- The overall model is network-based. DHT is a major upstream driver, but its effects are translated through several interacting pathways.
Frequently Asked QuestionsHair Follicle Biology and Hair Loss
TransparencyLimitations of the Review
This is a narrative literature review rather than a formal systematic review or meta-analysis. Much of the mechanistic evidence comes from cultured cells and animal models. These models are useful for testing pathways but do not establish the same effects in humans.
AGA is genetically heterogeneous, and the molecular response to androgens differs between follicle types and scalp regions. Inflammation, oxidative stress and vascular changes may be important in subsets of patients, but the literature does not support treating any one of them as the single cause of androgenetic alopecia.
Pathway studies also use experimental concentrations and interventions that may not correspond to commercial topical products. Wnt, BMP and TGF-beta signalling can have different effects depending on timing, cell type and tissue compartment. An experimental intervention that changes a pathway and induces hair growth does not by itself establish a safe or effective clinical treatment.
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Lustrao Research
The Biology Behind Hair Growth
Explore Lustrao Hair Regrowth Oil and continue through the evidence behind the ingredients discussed across the Lustrao research series.
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