This kind of rash can be contact dermatitis or hives. Hives (medically known as urticaria) are red, raised areas of skin that appear in varying shapes and sizes. They have a tendency to change size rapidly and to move around, disappearing in one place and reappearing in other places, often in a matter of hours. Apply calamine lotion or some mild steroid cream and also give some Benadryl( causes drowsiness) and Claritin. If the symptoms persist then a dermatologist’s evaluation will be the best.
I hope it helps. Take care and please do keep me posted in case you have any additional doubts. Kind regards.