Believe it or not, some people in the world are “allergic” to the sun. Erythropoietic porphyria is a rare, inherited disorder characterized by an abnormal response of the skin and painful reactions after periods of exposure to sunlight.

Allergy to the Sun?

Biologically, erythropoietic porphyria (EPP) is not a true allergic disorder. The pathophysiology of EPP is related to the abnormal increased amount of porphyrins in the body.

Heme, which is an integral part of hemoglobin, is produced in a step-by-step manner. It is commonly synthesized in the liver and the bone marrow. Just like an assembly line, in order to produce heme, porphyrin, the precursor of heme, is altered each step of the production line by certain enzymes. Because of a defect of the enzyme on the last stage of heme production, porphyrin builds up and reaches toxic levels causing nerve damage, hence pain. Light energy (from artificial or natural sources) excites porphyrins (protoporphyrins) and causes photosensitivity—burning, itching, and painful swelling of the skin especially in areas that are prone to sunlight exposure (face, ears, hands and feet). Blistering and edema occur as a result of prolonged exposure. Furthermore, the excess porphyrin escapes through the liver and into bile. This makes the person predisposed to formation of gallstones. Further deposition could cause liver dysfunction and eventually liver cirrhosis and enlargement of both liver and spleen. Abnormal amounts in the urine could also produce a port wine appearance. Neurological dysfunctions are also noted in some cases.

What your Doctor can do for you

Because the disorder is not that common, the possibility of porphyria is often overlooked. Family history of the condition is very useful to establish the diagnosis. Without this, blood, stool, and urine tests would reveal abnormal levels of protoporphyrin. To conclude the diagnosis, spectroscopy would detect the quantity of protoporphyrin at any fluid samples of the individual. The molecules would absorb light and glow in the sample, and the spectrofluorometer will determine the amount of fluorescence. In cases of hepatic problems, a liver biopsy may be needed.

The patient is advised to protect the skin from sunlight (or even artificial light) by covering up with protective clothing. Sunscreens have little or no effect at all. Zinc oxide (Calamine) however, blocks UV light. Currently, the development of the drug afemelanotide is underway. This drug has shown to induce melanin production in the skin subsequently reducing the harmful effects of UV rays.

Antihistamines have little effect on the reduction of symptoms. Beta-carotene could possibly decrease photosensitivity to some individuals. Transfusion of blood products or Heme analogues decreases the overproduction of protoporphyrin. In the event of gallstone formation, Ursodiol is prescribed; surgical intervention may sometimes be necessary.  Liver failure may need additional medications or liver transplant.

What you can do

People with EPP are advised to avoid sunlight as much as possible, and to apply sunscreens/ zinc oxide over the skin. Itchiness is usually unrelieved by antihistamines, and sometimes the only way to relief is rubbing the area with ice. The condition cannot be entirely cured, but can be managed by different drugs and medical procedures. Hence, relief of symptoms is the primary goal of medical management.