Milia are tiny (1-3 mm), superficially located epidermal inclusion cysts. They typically have a characteristic porcelain-white color. One often encounters a patient with a solitary milium or multiple milia. These tiny skin growths are entirely benign and cause no harm to the patient.
Clinical Findings: Milia are tiny epidermal inclusion cysts located superficially in the epidermis. They do not have an appreciable overlying central punctum. They occur in all races, at all ages, and equally in males and females. Primary milia occur without an underlying skin disorder. Secondary milia occur because of an underlying skin disorder, most often a subepidermal blistering condition. As the subepidermal blister heals, it is not uncommon to see the development of milia in the area of the previous blister. As an example, patients with porphyria cutanea tarda develop subepidermal blisters and typically heal with scarring and milia formation. Occasionally, a milium can have a somewhat translucent appearance and should be biopsied to rule out a basal cell carcinoma or an intradermal nevus.
In adults, milia most commonly occur on or around the eyelids. Up to half of all newborns have milia. These are typically located on the head and are termed more specifically congenital milia. They almost always resolve on their own without therapy, and therapy should be withheld to provide time for spontaneous resolution. Unique forms of milia eruptions have been described in the literature, including eruptive multiple milia, grouped milia, and generalized milia. Eruptive milia manifest over a period of weeks, with the appearance of 10 to 100 milia. This has been described in teenagers and adults. Grouped milia and milia en plaque are rare; these terms are used, respectively, to describe a nodular grouping and a plaque-like grouping of milia.
Certain genetic syndromes show an association with milia, the best recognized one being Bazek’s syndrome. This syndrome is defined as a constellation of milia, basal cell carcinomas, hypotrichosis, and follicular atrophoderma. A few other genetic syndromes that have milia are the Rombo syndrome, familial milia syndrome, and atrichia with papular lesions. Many other syndromes with milia have been reported.
Histology: Milia are tiny cysts in the superficial epidermis. The cyst has a true lining of stratified squamous epithelium. A granular cell layer is present in the cyst wall lining. The center of the cyst is filled with a small amount of keratin debris. There is typically no surrounding inflammation in a primary milium.
Pathogenesis: The cause is unknown, but the cysts are believed to be derived from the hair follicle, sebaceous gland, or eccrine gland epithelium. Secondary milia occur after subepidermal blistering or trauma that interrupts the epidermal-dermal junction.
Treatment: No therapy is required. Most milia are found during routine skin examinations and are brought to the attention of the patient for education. Patients are often unaware of the milia. If a patient is bothered by the appearance of the cyst, extraction with a comedone extractor after creating a tiny (1-mm) incision with a no. 11 blade is all that is required for removal. Once the cyst is removed, it almost never recurs, although other milia may develop after extraction. Treatment of congenital milia in infants is not equired because they almost all resolve spontaneously.