Seraphiel- I agree to dis agre there are genetic dis-orders, that cause it, this was pulled from stanford medical journal, 3 yrs ago they call it porphyria "The porphyrias are a group of rare inherited or acquired disorders of certain enzymes that normally participate in the production of porphyrins and heme. They manifest with either neurological complications or skin problems, or occasionally both.
Porphyrias are classified in two ways, by symptoms and by pathophysiology. Symptomatically, acute porphyrias primarily present with nervous system involvement, often with severe abdominal pain, vomiting, neuropathy and mental disturbances. Cutaneous porphyrias present with skin manifestations often after exposure to sun due to the accumulation of excess porphyrins near the surface of the skin.[1] Physiologically, porphyrias are classified as hepatic or erythropoietic based on the sites of accumulation of heme precursors, either in the liver or bone marrow and red blood cells.[1]
The term "porphyria" is derived from the Greek πορφύρα, porphyra, meaning "purple pigment". The name is likely to have been a reference to the purple discolouration of feces and urine when exposed to light in patients during an attack.[2] Although original descriptions are attributed to Hippocrates, the disease was first explained biochemically by Felix Hoppe-Seyler in 1871,[3] and acute porphyrias were described by the Dutch physician Barend Stokvis in 1889.[2][4]"
Cited via wikipedia , Web MD
http://en.wikipedia.org/wiki/Porphyria
http://www.webmd.com/a-to-z-guides/porphyria-10646
