If he is dairy-intolerant, he won't be able to digest the milk products (possibly yogurt, but even that can be a problem for some kids), so they'll go right thru him and yes, can burn the bum. To be sure, you'd have to do a dairy-free trial for a couple of weeks; it takes 2 weeks for dairy to clear the system, although you might see results much sooner and know from that to just stay off it and maybe try some again in another 3-6 months.