Milia are benign, asymptomatic, small, subepidermal, keratinous cysts found in individuals of all ages, most often on the face (Figs. 29-1, 29-2, 29-3). Milia appear as tiny (1 to 2 mm), white, raised, round lesions covered by a thinned epidermis found primarily on the cheeks and eyelids. No orifice can be seen. Some cases of idiopathic calcinosis cutis and syringomas may clinically mimic milia.

Primary milia are noninflammatory collections of lamellated keratin most frequently found within the undifferentiated sebaceous cells that surround vellus hair follicles. Milia found in infants tend to disappear spontaneously in a few months, but lesions in adults can be chronic. Most arise spontaneously, but others may be localized in areas of damaged skin associated with bullous disease such as porphyria cutanea tarda, bullous lupus erythematosus, and epidermolysis bullosa. Milia may also arise in areas treated by dermabrasion, laser resurfacing, and, rarely, at the site of radiation therapy. These secondary milia arise predominantly from eccrine duct epithelium.