Scientists at the University of Pennsylvania have discovered what makes men lose their hair and are narrowing in on a possible treatment.

Skin cells, brain cells and, yes, hair all have natural growth cycles. They grow, die and are replaced by newer models. But in the case of the 80% of Caucasian men who develop male pattern baldness at some point in their lives, hair follicles just stop re-growing.

Research done at the University of Pennsylvania by Dr. Luis Garza, now an assistant professor of dermatology at Johns Hopkins, found that during the natural cycle of hair growth, levels of a molecule called Prostaglandin D2, or PGD2, increase around a hair follicle just before it gives up the ghost. This suggested that PGD2 naturally inhibits hair growth.

When those scientists turned their sights on bald men’s pates, they found men with male pattern baldness had higher levels of PGD2 than their hirsute brethren and realized that the molecule, when told by bum genetics to overproduce, was most likely the cause of men’s receding hairlines.

To test their theory, the scientists isolated hair follicles from face- and brow-lift tissue obtained from plastic surgeons and hit them with PGD2. The more PGD2 the follicles received, the balder the skin.

Luckily, these scientists identified a receptor that triggers the molecule’s destructive habits. All the scientists would have to do then is use this receptor to create a treatment that will allow men in the early stages of baldness to hold on to their proud manes.

How might this work?

The shrunken follicles on bald men’s scalps allow thin, weak hairs to grow for a few days or a few weeks at the most before they fall out. By introducing a kind of decoy molecule onto the scene, the receptor would bind to the decoy and leave the PGD2 molecule alone. Without its trigger, PGD2 can’t do lasting damage to the follicle, giving the hair the same kind of time — usually around three years — to thicken and grow as hair has on non-bald scalps.

A handful of treatments that focus on the receptor are already in clinical trials, like the drug ramatroban. Trouble is, they’re all being used to fight asthma. PGD2, it seems, is a very busy nuisance. Not only is it the enemy of hair, it causes the bronchial contractions experienced by asthmatics. So chemists are now at work trying to figure out a way to turn oral and inhalable drugs into topical ones.

There is no known relationship between asthma and male pattern baldness. Having one condition does not put you at any particular risk of the other, as PGD2 works a little differently in the two. The enzymes that create PGD2 on the scalp come from the brain, while PGD2 in the lungs is blood-born. People who suffer from asthma go into PGD2 production overdrive when they come into contact with an allergen. The PGD2 leads to inflammation, and the person has trouble breathing. As far as scientist know, though, their hair remains perfect.

Simply inhaling asthma medicine doesn’t seem to have much of an effect on thinning hairlines. But the study does shed some new light on how certain anti-baldness drugs might work.

Current FDA-approved medications for the treatment of male pattern baldness are a lotion containing minoxidil and a pill containing finasteride.

Originally conceived as a high-blood-pressure treatment, minoxidil’s ability to halt hair loss is largely a mystery. One possible explanation is that the drug is known to increase the production of the molecule PGE2, a known promoter of hair growth sorely lacking on the scalps of bald men. The University of Pennsylvania scientists are interested in finding out whether minoxidil also decreases PGD2, though they are not actively studying the link.

So, how long before bald men see some relief? Unfortunately, there’s no timetable. They have to figure out dosage and safety before clinical trials even begin — and those could take years.

And scientists aren’t sure if the drug can only be used preventively — that it won’t work on men who have already lost their hair. So, middle-aged guys, you could be the last, very annoyed group of bald men in human history.