Contact dermatitis can be due to allergies, but, more commonly, it involves inflammation resulting from contact with an irritant -- usually acids, soaps and detergents, solvents, or other chemicals. The reaction usually resembles a chemical burn. There are several pictures of contact dermatitis reactions here.Have you tried switching your son's shampoo, bath soap or the detergent you use to wash his clothes and sheets?   It still seems odd that this only affects one eyelid. Did your doctor do a patch test on your son? Patch testing is the gold standard for this kind of problem. It's used for patients who have chronic, recurring contact dermatitis. It requires three office visits and must be done by a clinician with detailed experience in the procedures and interpretation of results. If there's anything that your son uses or is exposed to that seems to cause the problem to happen, you should bring that with you to the doctor for the test. If your doctor didn't do a patch test, you might want to ask about this one.   It may also be some sort of infection in the skin. Check out this page about skin rashes, which offers some suggestions on how to relieve them. If your son's problem isn't getting better, then your doctor has got to help you find a solution.