Primary milia arise in infants most commonly, but also can occur in children and adults. Secondary milia are seen in a number of blistering disorders and following dermabrasion. Milia are tiny epidermoid cysts. The cysts may be derived from the pilosebaceous follicle. Primary milia arise on facial skin bearing vellus hair follicles.
Secondary milia result from damage to the pilosebaceous unit.
Milia en plaque is very rare with less than 20 case reports in the world literature. Multiple eruptive milia also are rare, but still more common than milia en plaque. No racial variations in incidence exist. Eruptive milia and milia en plaque occur more frequently in women. Primary milia in newborn infants are so common that they can be considered normal.