Cutaneous lesions which are indicative of various forms of metabolic disturbance have been identified and studied so that lesions of lipid metabolism, diabetes, glandular dysfunction, etc., are recognized and are often of great diagnostic assistance. Abnormal porphyrin metabolism also is at times manifest by skin lesions, and photosensitivity is considered a contributing factor; thus one readily understands why skin lesions due to light sensitivity and the cutaneous signs of porphyria were considered to be related.
Various eruptions due to sensitivity to light have long been known, and investigators searched for a sensitizer, which they concluded was a product of metabolism or derived from ingested substances. Bazin in 1862 and Hutchinson in 1888, respectively, described hydroa aestivale and summer eruption. It is interesting to note that those keen observers discussed the eruptions under consideration in relation to herpes simplex, simple prurigo, and erythema multiforme, for they