The mode of inheritance is autosomal dominant. An increased incidence of colloid milium has been reported in oil refinery workers in the tropics. This may represent interplay between light and petroleum constituents. Phenols have been suggested as causative agents. Prolonged use of hydroquinones has been reported to cause colloid milium in association with ochronosis.
Light microscopy is the definitive investigation.
Electron microscopy may be necessary to distinguish between colloid and amyloid. These conditions can look very similar on light microscopy. Typically, fissured eosinophilic colloid masses are seen in the dermis. Solar elastosis is marked. These changes are more pronounced in the nodular form with the vast majority of the dermis filled with amorphous colloid.