The
anagen phase of the hair cycle describes the growth phase of the hair follicle during which time the keratinocytes in the hair matrix are undergoing very high metabolic activity. Chemotherapy drugs that affect the high cell turnover of cancer cells can have direct toxic effects on the rapidly growing anagen hairs, leading to weakening of the hair shaft with abrupt interruption of growth and consequent abnormal breakage patterns along these weakened shafts.