Male pattern baldness: What causes it?

Why do so many men go bald? What exactly changes on their heads? Hot off the lab bench: Men go bald because the follicles from which their hairs sprout run out of special progenitor cells with which to make the hair.

Normally, inside hair follicles a region called “the bulge” contains a packet of adult stem cells from which the hair is replenished. Scientists have theorized that these stem cells might simply run out in those prone to male-pattern baldness.  

To test this, a team of researchers at the University of Pennsylvania (and, it seems, a few other places) looked at hair follicles from discarded bits of scalp from 54 men seeking hair transplants. Comparing the follicles from still-hairy samples of these scalps with non-hairy samples, the researchers  found:

1) The hair follicle stem cells were still there


2) Another set of cells — known as hair progenitor stem cells — were depleted.

The scientists concluded that somehow, for some reason, the stem cells don’t transform into progenitor cells anymore. That makes male-pattern baldness similar to alopecia areata, a reversible kind of hair loss.

All well and good, but what does that mean for a person who has lost his hair and wants it back? Maybe nothing right now, but the scientists do note that the results suggest “potential reversibility of this condition.” And, they add, these and their other findings suggest the hair follicle is a fairly complicated place. The new info should help them develop therapies down the road for a range of hair and skin disorders.

Here’s more about hair biology: Read the study in its entirety in the Journal of Clinical Investigation.