Prurigo nodularis is a health condition that causes itchy, hard and crusty lumps to develop on the surface of the skin, as stated by the American Osteopathic College of Dermatology. Itching caused by prurigo nodularis can last all day, but it occurs primarily at night and will not subside until a person scratches themselves to the point of feeling pain or bleeding.
Sores that form as a result of prurigo nodularis tend to be rough and dry on top and hard around the edges. They can be about a half inch wide and often leave behind white colored scars as they age. Prurigo nodularis is primarily caused by excessive scratching. As a result of excessive scratching, nerves on the skin become thick and respond to stimuli by sending abnormally strong itch signals.