The etiology of alopecia areata (AA) is unknown, but it is presumed to result from an autoimmune reaction. Thyroid abnormalities are increased in AA, but levothyroxine sodium replacement therapy does not induce hair regrowth.1 Calcitonin gene–related peptide (CGRP) is a 37–amino acid peptide produced by thyroid C cells. Calcitonin gene–related peptide is the most powerful cutaneous vasodilator known and is present in peripheral sensory nerves, the central nervous system, splanchnic organs, and around eccrine glands.2 Calcitonin gene–related peptide preferentially vasodilates the head, neck, upper part of the trunk, and upper arms.
Daly TJ. Alopecia Areata Has Low Plasma Levels of the Vasodilator/Immunomodulator Calcitonin Gene–Related Peptide. Arch Dermatol. 1998;134(9):1164-1165. doi: