Prostaglandin D2 (PGD2) appears to inhibit hair growth in androgenetic alopecia (AGA) and may be potential target for its treatment, new research suggests (Sci Transl Med. 4(126):126ra34). Researchers show that PGD2 inhibits hair growth in explanted human hair follicles and when applied topically to mice. Prostaglandin D2 synthase (PTGDS) is elevated at the mRNA and protein levels in bald scalp compared to hairy scalp of men with AGA. During normal follicle cycling in mice, PTGDS and PGD2 levels increase immediately preceding the regression phase, suggesting an inhibitory effect on hair growth. In transgenic mouse, K14-Ptgs2, which targets prostaglandin-endoperoxide synthase 2 expression to the skin, was shown to produce elevated levels of PGD2 in the skin and led to alopecia, follicular miniaturization, and sebaceous gland hyperplasia—hallmarks of human androgenetic alopecia. The authors urge further study of PGD2 inhibition to treat AGA.