Hello, Most common cause for a red,raised and itchy rash could be allergy.The Diphenhydramine content in Benadryl would have taken care of the rash for a while.Most important thing to know in a case of allergy is to find out the thing to which your son is allergic. If such child is brought to my clinic ,i would ask the following questions to elicit the cause *Exposure to any known allergen(could be dust,cold,foods like egg,milk,or fish) *Exposure to any new cosmetic or food *Insect bite *Family history of allergy or Asthma It can be assured that he will be fine.But if you find out the cause,then you must take care that your son must not be exposed to the allergen As the rash got spread to different parts of the body its better that he is seen by your physician for immediate care.