It sounds like exzema. Exzema can flare up due to food allergies, or topical allergies, or just because it wants to. If you as a mom notice a connection then I would avoid yogurt. Some children can outgrow exzema. There are other options other than cows stuff. Goat milk milk is a good alternative and may help the problem. As far as yogurt, there is yogurt made out of coconut milk that may not cause his exzema to flare up. If you are really concerned you can also take him to a dermatologist. Good luck!