Got scars? As you've no doubt noticed, scar tissue is distinct from normal skin.
It's more taut, and it's hairless. When scar tissue patches up a wound, it doesn't replace lost hair follicles. Not a big deal if the scar in question is minuscule and resides, say, on your elbow. However if it's located on your scalp, it could be quite a nuisance.
There is some good news. Scientists noticed that in some mice, if the scar met a minimum size, hair grew back after all. This meant that new hair follicles were being generated in these mice. The only cell type that can pull off such a feat is a stem cell.
Scientists studied the mice to figure out how this was happening, and found that the source of the new hair follicles wasn't hair follicle stem cells, as expected, but epidermal stem cells. This is surprising because adult stem cells are typically more limited in the types of cells they can produce. Only a hair follicle stem cell would be expected to be able to generate all the cell types needed to build a hair follicle.
Upon further study, scientists discovered that a protein important in hair follicle development, Wnt, was present in mice that grew hair in their wounds, and not present in mice that did not. This is useful information for people suffering unwanted bald patches from scars.
Scientists may be able to use this protein to help people grow new hair follicles. The one downside is that the new hair follicles in mice lack melanocytes, the cells that give hair its color. Then again, if scientists can manage to help people grow new hair follicles, adding pigment may be small potatoes.