What Causes Eczema?

Hi!! I ve been told by a dermatologist that I have eczema. The steroid cream seems to be ineffective. When I apply it ,it seems to turn into a crumbly mess. It tones it down but never clears it up. I ve had this eczema on my upper back for over a year and have tried various creams and ointments over the counter. The problem is I don t have itching....but of course it looks awful...feels awful...and theirs this thick layer of skin that forms over a few spots on my back....I try not to but I pick at it than apply cream...the thick skin just keeps forming. Its definatly not a typical scab like you d get having a sore. I m wondering what is causing this...laundry detergent?? Medication I m taking?? I just want it to go away!!!