This condition was originally described by Unna as occurring in sailors who were much exposed to weather and sun. The condition, as will be shown later, is not confined to seafaring men, but also occurs in farmers and those who are exposed to a dry climate and excessive actinic rays. In both of these groups of cases there is an acquired hypersusceptibility to actinic rays, as opposed to the congenital intolerance that appears to be the basis of xeroderma pigmentosum.

There first appears upon the exposed parts a diffuse cyanotic redness. Pigment spots soon appear, but the areas between these "freckles" may or may not lose their pigment. Telangiectases appear, and the skin becomes dry and hard, and keratoses usually result. This condition may last for years, but usually there develop basal-celled carcinomata, that run the clinical course of rodent ulcers.

When this condition begins to develop, the patient should give up an out-of-door life, or at least protect himself from light. In the later stages the treatment consists of the surgical removal of the growths.