How do you cure dry, irritated skin on a dog?

My eight-month-old black Lab, Aspen, recently had a bad flea infestation, that, thankfully, seems to be almost completely gone. The problem is, the fleas were so thick on him for so long, they left his skin red and irritated. The biggest problem areas are his undercarriage (base of chin to under tail), "arm" pits, and the underside of his ears. In the places where it's not flaky, his coat is sparse and coarse. It's not /really/ bad as far as the coat goes, but it is thinning pretty quickly - he's still shedding even though his winter coat is 98% gone. So is there anything I can apply to his skin/coat to get rid of the irritation? Natural remedies are preferred - I don't like the idea of making his skin absorb chemicals and such, which can cause liver and kidney failure as he gets older.