Aversion to Sunlight

The effects of these diseases, if left untreated, can be devastating.
The malfunctions in the body's chemistry cause the skin to be extraordinarily sensitive to sunlight, with a result that exposure to even mild sunlight can disfigure the skin, cause the nose and fingers to fall off, and make the lips and gums so taut that the teeth, although no larger than ordinary, look like they are jutting out in a menacing, animal-like manner.

The chief defense against the painful effects of the sun, Dr. Dolphin http://query.nytimes.com/gst/fullpage.html?sec=health&res=9C0CE7D71739F9...
suggested, would be to venture forth only at night, as werewolves(DaRuDe) and vampires(ME :p) were said to do.
Some victims of the disease also become very hairy, he said, conceivably one of nature's efforts to protect the skin from the sun.