External Light Activates Hair Follicle Stem Cells Through Eyes Via an ipRGC–SCN–Sympathetic Neural Pathway

June 2018 in “ Proceedings of the National Academy of Sciences of the United States of America ”

Shih‐Kang Fan, Yu-Hao Chang, Chih-Lung Chen, Wei‐Hung Wang, Ming‐Kai Pan, Wen-Pin Chen, Wen‐Yen Huang, Zijian Xu, Hai-En Huang, Ting Chen, Maksim V. Plikus, Shih‐Kuo Chen, Sung‐Jan Lin

hair follicle stem cells intrinsically photosensitive retinal ganglion cells ipRGCs suprachiasmatic nucleus SCN sympathetic neural pathway norepinephrine autonomic nervous activity hair stem cells retinal ganglion cells sympathetic nervous system adrenaline

TLDR Light can turn on hair growth cells through a nerve path starting in the eyes.

The study from June 29, 2018, demonstrated that external light can activate hair follicle stem cells through a neural pathway that begins with the stimulation of intrinsically photosensitive retinal ganglion cells (ipRGCs) in the eyes. Following light stimulation, ipRGCs trigger the suprachiasmatic nucleus (SCN), which in turn activates systemic sympathetic activities. These activities lead to the release of norepinephrine in the skin, which activates hair follicle stem cells. This finding reveals a novel function of ipRGCs in regulating autonomic nervous activity and illustrates how the body can rapidly respond to external light stimuli, potentially affecting not just hair follicles but other organs as well.

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