Acute radiodermatitis occurs when an "erythema dose" of ionizing radiation is given to the skin, after which visible erythema appears up to 24hrs after. Radiation dermatitis generally manifests within a few weeks after the start of radiotherapy. Acute radiodermatitis, while presenting as red patches, may sometimes also present with desquamation

Desquamation

Desquamation , also called skin peeling, is the shedding of the outermost membrane or layer of a tissue, such as the skin.-Skin:Normal, nonpathologic desquamation of the skin occurs when keratinocytes, after moving apically over about 14 days, are individually shed unnoticeably...

or blistering. Erythema may occur at a dose of 2 Gy radiation or greater.