my baby has allergies to his flea shampoo

(and fleas) and he breaks out in red welts... we are flea free, but when i used the shampoo on him after i would visit my moms house he would have these red spots all over his tummy area. and you could feel that the skin was different, almost like a blister.... obviously it was an allergic reaction, so we had to stop using the shampoo and it cleared up right away... could you take a picture so we could see what you are describing?