It's just like a human being with allergies. The body produces a histimine that can cause rashes, hives, intense itching, and swelling of airways and bronchi plus a host of other symptoms. Also in humans peanuts allergies have been so severe as to cause death. I have a little Lovie Chotu, who does much better, way less plucking, as long as he stays on a corn free diet. The minute he eats anything with corn in it he start's pulling out his feathers furiously. He still plucks a little bit on the base of his tail, but he's stopped plucking the tops and bottoms of his wings. (Knock on wood).
Plucking is such a complex issue. It's always best to start with medical investigation like giardia, or crop infection or any other kind of illness and rule those out. If you can rule out the medical you can start on the psychological reasons. Lack of flight, phobias, fear of certain things or objects, cage placement, not enough natural sunlight, hormonal, etc... etc....
Ginger
