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.
Skin biopsy is necessary only if the diagnosis is in doubt.
The histological features are identical to those of epidermoid cysts, but the cysts are much smaller. It contains a variable amount of lamellated keratin. The common primary milia found in infants and children are found in the undifferentiated sebaceous hair collar surrounding vellus hair follicles. Milia secondary to blistering often are found in eccrine sweat ducts. No topical or systemic medications have any effect on primary and secondary milia.