 A 2012 research paper indicates a causal link between elevated levels of localized PGD2 and hair growth inhibition.Applied topically, the researchers found PGD2 prevents hair growth, and mice that were genetically inclined to produce higher levels of PGD2 had inhibited hair growth.The researchers also found PGD2 levels were much higher in balding scalp tissue than nonbalding scalp tissue, through increased levels of prostaglandin D2 synthase.