Prostaglandins and Hair: The PGD2 Discovery That Reframed Balding

PGD2 in balding scalp is three times higher than in non-balding scalp. It inhibits hair growth through the PTGDR2 receptor. This discovery opened an entirely new therapeutic target — and a drug class that continues in development.

The identification of prostaglandin D2 as a hair growth inhibitor elevated in balding scalp was one of the more significant findings in AGA biology of the 2010s. It expanded the mechanistic framework beyond DHT and androgens into lipid signalling, and it opened a pharmacological target class — PTGDR2 antagonism — that continues in development.

The Garza 2012 findings

Luis Garza and colleagues at Johns Hopkins performed a proteomic comparison of balding and non-balding scalp from the same men undergoing hair transplantation. The spatial advantage of comparing adjacent zones in the same person controlled for interindividual variation. The result: PGD2 was approximately three times higher in balding vertex scalp than in non-balding occipital scalp. PTGDR2 receptor expression was similarly elevated.

Mechanistic validation in murine and organ-culture models confirmed that PGD2 inhibited anagen through PTGDR2 — mice overexpressing prostaglandin D synthase developed AGA-like patterned hair loss.

PGD2 mechanism at the follicle

PGD2 binding to PTGDR2 on follicle cells (particularly in the outer root sheath and DP) activates signalling cascades that reduce anagen-sustaining pathway activity. Specifically, PTGDR2 activation appears to suppress Wnt signalling and to upregulate catagen-initiating signals including TGF-beta. The net effect is accelerated anagen termination — a shortened growth phase that mirrors the core biology of DHT-driven AGA.

Why PGD2 is elevated in balding scalp remains partially unclear. Androgen signalling likely upregulates prostaglandin D synthase in susceptible scalp, creating a secondary amplification loop where DHT drives both direct DP signalling and indirect PGD2 elevation. The two pathways may synergise to produce the clinical severity of AGA.

The contrasting prostaglandins

The biphasic nature of prostaglandin effects on hair growth is pharmacologically relevant. PGE2 (prostaglandin E2) and PGF2-alpha analogues have growth-promoting effects on hair follicles through their own receptors (EP and FP receptors). Bimatoprost, a prostaglandin F analogue, produces eyelash growth robustly enough for FDA approval. Latanoprost applied to the scalp has been studied with modest positive results in small AGA trials. The therapeutic logic: block the inhibitory prostaglandin (PGD2/PTGDR2) or activate the growth-promoting ones (PGE2, PGF2-alpha/EP or FP receptors).

Clinical translation status

Setipiprant (Allergan/Cassiopea) advanced furthest in PTGDR2 antagonism for AGA, completing Phase 2a. Results were positive for some endpoints but the development programme was paused for commercial reasons rather than safety signals. Second-generation PTGDR2 antagonists with better pharmacological profiles are in earlier stages. The PGD2 pathway remains a validated target even without an approved drug.