Cline D J
University of Cincinnati College of Medicine, Ohio.
Dermatol Clin. 1988 Apr;6(2):295-303.
Hair color changes result not only from alterations of melanin production but also from changes in the hair structure itself, altering its optical properties. A variety of genetic, metabolic, nutritional, and acquired disorders result in hair color changes. When the underlying defect can be corrected, hair color usually returns to normal. The flag sign can occur as a result of nutritional insults or due to medications. Most drug-induced changes in hair color result in lighter hair color, although PABA and some chemotherapy regimens have darkened hair. Green hair due to exogenous copper may be associated with prior damage to the hair cuticle. Alopecia areata may selectively involve pigmented hairs. Regrowing white hairs have shown both keratinocyte and melanocyte abnormalities. Gray hair may temporarily darken after inflammatory processes, after electron-beam-induced alopecia, and after some chemotherapy regimens. Much remains to be learned about the physiology of human graying.
头发颜色的改变不仅源于黑色素生成的变化，还源于头发结构本身的改变，从而改变其光学特性。多种遗传、代谢、营养和后天性疾病都会导致头发颜色改变。当潜在缺陷得以纠正时，头发颜色通常会恢复正常。“旗标征”可能是营养损伤或药物所致。大多数药物引起的头发颜色变化会导致头发变浅，尽管对氨基苯甲酸（PABA）和一些化疗方案会使头发变黑。因外源性铜导致的绿色头发可能与之前的毛小皮损伤有关。斑秃可能会选择性累及有色头发。再生的白发显示出角质形成细胞和黑素细胞均异常。在炎症过程后、电子束诱发脱发后以及一些化疗方案后，白发可能会暂时变黑。关于人类头发变白的生理机制，仍有许多有待了解之处。
