There are many external and internal triggers for itching including medications, dry skin, dermatitis, medical conditions, etc. When the scratching is particularly severe, the skin may thicken and form a leathery patch or plaque which is referred to as lichen simplex chronicus. Another form of skin reaction to itching is prurigo nodularis where large, itchy nodules appear, most of the time on the outside of the arms or legs.  There are many treatments for itching, including phototherapy, antihistamines, and a variety of topical therapies. Testing may need to be performed to look for underlying triggers for the itching.