Some of my family are plagued with eczema from childhood - it seems to be hereditary but not always passed (my niece has twins - one has it the other doesn't). I don't think there is a really effective cure yet - I wish there was.
I don't know how old your son is but I knew a young man in his mid twenties who had bad eczema on his face. After he gave up smoking, it cleared up.
I thought it was worth a mention for anyone who smokes. ( not saying your son smokes of course)
My nephew suffered badly from this, but he eventually grew out of it in his mid-20s. He did have medically prescribed creams and shampoos which helped a lot until then. I don't know if this helps at all.