Radiation-induced alopecia commonly follows therapeutic radiation for head and neck cancers, and sometimes follows diagnostic radiology exams when patients inadvertently are overdosed. Recent overdosing during CT brain perfusion scans has brought attention to radiation-induced alopecia. Host biologic factors such as age, tissue hypoxemia, genetic factors, and nutrition factors interplay with exposure-related factors such as dose fractionation, dose rate, and the size of the radiation window to determine the severity of the tissue injury. Radiation-induced alopecia is anagen alopecia; hair loss occurs during the growing phase of the hair cycle. High-dose radiation can obliterate hair follicles, resulting in permanent alopecia.

Before systemic antifungal agents were available, whole scalp radiation therapy was commonly used to treat tinea capitis (fungal infection of the scalp) by the purposeful induction of alopecia. Long-term follow-up of these patients has shown an increased incidence of skin cancers and even brain malignancies.