In research published in Cell, Ya-chieh Hsu, professor of stem cell and regenerative biology, and her lab found that the hair loss resulted from a two-part reaction.

How stress triggers immediate hair loss

The first part, the immediate loss of hair, was simple. “Stress has an immediate impact through the activation of the sympathetic nervous system,” explained Hsu, who is also a principal faculty member of the Harvard Stem Cell Institute.

She said that it begins with our natural “fight or flight” response, which releases norepinephrine, a neurotransmitter that—among other effects—kills highly proliferating cells in the hair follicle when the level is too high.