Scientists Think They’ve Found The Cause For Gray And Balding Hair – Huffington post (press release) (blog)

According to the study, stem cell factor or SCF, is a protein “essential for hair pigmentation.” When it’s not present, hair turns gray or white. While the scientists already knew that, these findings show what happens “after those stem cells move down to the base, or bulb of hair follicles and which cells in the hair follicles produce SCF.”