How Does Hair Know When to Stop Growing?

The hair on your scalp can get really long, but your leg hair doesn’t sweep the floor. Why not?

Hosted by: Hank Green
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Sources:http://www.webmd.com/skin-problems-and-treatments/hair-loss/science-hair?page=2
https://www.aad.org/dermatology-a-to-z/for-kids/about-hair/how-hair-grows
http://www.loc.gov/rr/scitech/mysteries/grayhair.html
http://physrev.physiology.org/content/81/1/449#ref-533
http://www.livestrong.com/article/109520-eyebrow-growth-rate/
http://stemcells.nih.gov/info/basics/pages/basics1.aspx
http://physrev.physiology.org/content/81/1/449#ref-533
http://news.yale.edu/2011/09/01/yale-scientists-find-stem-cells-tell-hair-its-time-grow

Видео How Does Hair Know When to Stop Growing? канала SciShow