This document discusses ultraviolet (UV) radiation, including its physical properties, physiological effects, and therapeutic uses. It notes that UV radiation is electromagnetic radiation with wavelengths between 290-400nm. Physiological effects include erythema (sunburn), thickening of the epidermis, pigmentation, and cancer. Therapeutic uses include treating acne, psoriasis, wounds, and alopecia. Proper application involves determining individual sensitivity, starting with suberythemal doses and gradually increasing based on the patient's response.