What are milia cysts exactly?

Keratin-filled cysts. Milia are very common, benign, keratin-filled cysts that appear as superficial, uniform, pearly-white to yellowish domed lesions measuring 1-2 mm in diameter, usually on the face, especially the nose. Primary milia are believed to arise in sebaceous glands that are not fully developed. No topical or systemic medications are effective on primary milia, and they tend to spontaneously disappear.