Secondary lesions arise following blistering or trauma, due to disruption of the sweat duct. Milia have been described in many disorders, including bullous pemphigoid, inherited and acquired epidermolysis bullosa, bullous lichen planus, porphyria cutanea tarda, and burns. Skin trauma from dermabrasion can result in milia formation. Radiotherapy that causes destruction of skin appendages can result in rings of milia at the periphery of the treated skin. Secondary milia have been described following potent topical corticosteroid use.
Milia are a feature of a number of very rare genodermatoses.
Both primary milia and multiple eruptive milia have been reported as familial disorders with autosomal dominant inheritance. The etiology of milia en plaque is unknown. No investigations are needed for simple milia. The clinical appearance is diagnostic. Investigation of the underlying disease is necessary in secondary milia.