Colloid milium is a rare degenerative condition related to sun exposure. It is marked by multiple domed, skin-colored papules developing on the sun-exposed skin of the face, ears, neck, dorsal hands, and forearms. Histologically, there is deposition of homogeneous eosinophilic colloid in the papillary dermis. There are 4 clinical variants: adult, juvenile, pigmented, and nodular.

Adult colloid milium is the most common clinical form and has a 4:1 male preponderance, while the juvenile form is very rare and has been attributed to both autosomal dominant and autosomal recessive patterns of inheritance. The juvenile form has its onset in the prepubertal years and appears to be due to an abnormal susceptibility of keratinocytes to damage from ultraviolet (UV) light.

Nodular and pigmented colloid milium are subsets of the adult type, with the nodular form exhibiting larger nodules and plaques, mostly on the face, while the pigmented variety presents with confluent gray-brown papules on the face.

In addition to sunlight, both petroleum and phenols have been associated with rare occurrences of colloid milium. Hydroquinone exposure with resultant exogenous ochronosis contributes to the pigmented form.

The lesions of colloid milium tend to reach a peak within 3 years, after which few new papules occur. The lesions do not resolve and occasionally may be pruritic.