The researchers suggest that defects in regulatory T cells could be a cause of alopecia areata and may also contribute to other forms of baldness.

Senior author Michael Rosenblum, an assistant professor of dermatology at UCSF, explains that hair follicles are continually regenerating. He says that "when a hair falls out, the whole hair follicle has to grow back."

Before this study, it was thought that stem cells were completely in charge of hair follicle recycling.

However, the new research reveals that regulatory T cells, commonly termed Tregs, are essential to hair follicle recycling.

"If you knock out this one immune cell type," says Prof. Rosenblum, "hair just doesn't grow."