When skin is wounded, the hair cannot regrow. In a recent study, researchers ask why this is and whether it can be reversed. They conclude that a signaling pathway called the sonic hedgehog may be critical.

Though it may seem simple, hair regrowth is complex and mysterious.

Hair loss comes in many forms. It can be a gradual, gene-driven loss known as male- or female-pattern baldness.

Alternately, it may result from an injury, such as a burn or deep wound.

However the hair has been lost, regrowing it is a technical challenge that has defied researchers since the dawn of science.

In ancient Egypt, for instance, there was a range of unusual regrowth techniques, including rubbing hippopotamus fat into the scalp.

Although science has moved on, it is still only inching toward a solution to hair loss.

The latest study to investigate regrowth was headed by cell biologist Mayumi Ito, Ph.D., an associate professor at the New York University Langone Health center in New York City.

Her team’s findings were published this week in the journal Nature Communications.