Chemotherapy causes hair loss because the drugs used in chemotherapy target and kill rapidly dividing cells. Hair follicle cells divide quickly as they produce growing hair, so they are unintentionally damaged by chemotherapy drugs. This leads to cell death in the hair follicles, causing hair to fall out. The process is largely due to apoptosis (programmed cell suicide) triggered in the hair follicle cells as a side effect of the treatment. Hair loss typically begins within 1 to 3 weeks of starting chemotherapy and is usually temporary, with hair regrowth starting a few weeks after the treatment ends. However, the extent of hair loss depends on the type and dose of chemotherapy drugs used and individual responses.
