Nobel Prize winning research 2016
Your cells of the hair can be destroyed to compensate for any need of Nutrients ( A phenomenon called autophagy ) or compensated failure. Dr. Yoshinori Oshumi from Japan was awarded the Noble Prize for Medicine in 2016 for his work on autophagy. If iron levels or amino acid levels are low, they will be restored by arresting the growth of the hair follicles. The levels are maintained normal by not making the hair. Therefore we can also assume that hair will grow only with total wellness.