Comedo formation in acne.

Comedones contain a considerable quantity of water. In some cases a water content of more than 40% can be detected. The comedo consists of two parts, an inner nucleus built up to unorganized materials and a capsule with concentrically arranged shells. The material of the nucleus contains small scales produced by normal keratinization. The materials of the capsule consists of larger scales, which result from hyperkeratosis. The nucleus of the comedo seems to be identical with the early comedo. A similar structure can be formed in vitro by adding water to sebum. Microorganisms have optimal growth conditions in the early comedo.