there can be many reason allergic to urine, diaper, dye n synthetic clothes, it's very hot n humid these days, we as an adult can do all kinds of medication on our body but wen it cums to kids let's not ignore. consult a pediatrician immediately.

Hi, can you plz share the picture so that we can ask expert.

may be allergic to some clothes material or not thoroughly clean I guess. can also be allergic to some medicine but then would have got on whole body . pls get him checked with doc.