Milia (singular, milium) are minute epidermoid cysts (also known as infundibular cysts) that present as small white or yellow papules, usually on the face. They are typically smaller than 3 mm in diameter. They occur when sloughed off skin becomes trapped in the dermis. There is no predilection for either sex or for any race or ethnicity.

Primary milia affect 40%-50% of newborns but may be found in patients of all ages.

Secondary milia often occur after cosmetic procedures (dermabrasion, chemical peels, ablative laser therapy) or trauma, or in conjunction with a number of blistering disorders. Milia may occur in tattoos. Patients with skin phototypes IV through VI tend to be more likely to develop milia as sequelae of chemical peels. Blistering disorders that may heal with milia and scarring include epidermolysis bullosa acquisita; porphyrias, including porphyria cutanea tarda; bullous pemphigoid; herpes zoster; contact dermatitis (allergic, irritant); bullous lupus erythematosus; and dermatitis herpetiformis. Milia have also been known to occur in areas of topical steroid-induced atrophy. Persistent or widespread milia are associated with a number of syndromes (see Differential Diagnosis & Pitfalls).

Milia en plaque refers to a rare entity that typically occurs in the periauricular area.