For my kids it seemed to be related to food sensitivities, so if I could keep consumption of the foods down it helped (one had problems with wheat, the other had problems with corn). And, yes, both passed through breastmilk enough to make a difference (at least in our case).
I bumped up their consumption of essential fatty acids, especially Omega-3...flaxseed oil is a good source. Buy it liquid (should be refrigerated) and you can mix it in with other stuff. I think Dr. Sears recommended mixing it with ketchup.
I didn't do much with external treatments. I've heard of soaking it with olive oil, then combing out; or, using oats in a mesh bag, dampen and rub over scalp, then comb out.