How the stress of fight or flight turns hair white

Abstract

Signalling from the sympathetic nervous system of mice subjected to stress leads to the depletion of a stem-cell population in their hair follicles. This discovery sheds light on why stress turns hair prematurely grey.

Keywords: Neuroscience; Physiology; Stem cells.

Figure 1 |. Melanocyte stem cells and stress.

Melanocyte stem cells (MeSCs) are located in the bulge of the hair follicle, which is innervated by sympathetic neurons that release the neurotransmitter molecule noradrenaline. The follicle cycles through three phases: regeneration (anagen), degeneration (catagen) and rest (telogen). a, Under normal conditions, MeSCs migrate away from the bulge (red arrows) and differentiate into melanocytes during anagen. Melanocytes synthesize pigments that add colour to the regenerating hair. During catagen and telogen, they begin to die and migrate out of the niche (not shown). However, plentiful MeSCs remain to replace the melanocytes in the next anagen phase. b, Zhang et al. show that stressful stimuli activate the sympathetic nervous system, increasing the release of noradrenaline in hair follicles. Noradrenaline causes complete conversion of MeSCs into melanocytes, which subsequently migrate out of the niche. The hair follicle is depleted of MeSCs that would have differentiated to replace these melanocytes. Without any pigment cells to colour the hair in the next anagen phase, it begins to look grey or white.