High levels of PGD2 present in asthma patients, so a plausible solution here is to inhibit PGD2, which is what Atopix therapeutics has done with OC459. The results are here:
Atopix site does not say it is specifically a PGD2 inhibitor. It is a CRTH2 receptor blocker, and PGD2 does bind to that receptor but it isn't the receptor in the hair follicle, the presentation says they tested 3 receptors and it is GPR44 receptor in the hair follicle which responds to PGD2 by inhibiting hair growth. They either need a GPR44 receptor antagonist, or something which blocks the COX2 enzyme from making the prostaglandin. But that might have wide ranging biological affects unless it is topical and doesn't become to systemic from absorption.