My friend's DS had V bad excema as well...her told her to give ds a bath for exactly 20 minutes every night in plain, lukewarm, not hot water, then at the end, wash hair with baby shampoo, and body with Dove soap (the pain white or for sensitive skin bar) then rise well...and apply lotion (something for sensative skin) within 3 monites of hetting out of the bath. Also, don't scrub, or rub skin, just pat with the towel.
He started clearing up within weeks.
Gook luck.