the DR said that it is some sort of allergy since the baby does not have any fever. she prescribed Zyrtec Syrup. After taking it for 3 days i do not see much change. I really want to know what caused the allergy, and have not been giving my baby `suspicious' foods, but still it is spreading. How long does it take to treat an allergy. Will the rash go away right after the 'cause' is treated?