The invention relates to compositions and methods for regulating hair growth. Specifically, the invention relates to regulating hair growth by regulating the activity one of the prostaglandin D2 (PGD2) receptors, DP-2 (GPR44). Compositions and methods for regulating hair growth include inhibiting hair growth by administering a DP-2 agonist, or stimulating hair growth by administering a DP-2 antagonist.