Thanks for posting your query at DoctorSpring.com. I can understand your concern.
This is urticaria, also known as hives.
It's a form of allergy, however it's difficult to find out to what is the allergy, it could be due to food, medicines, dust, pollen, animal dander etc.
I would recommend that you administer the baby an anti histamine like hydroxyzine drops in the dose recommended by your pediatrician.
Application of calamine lotion will soothe any itching if present. The drops will resolve the allergy.
Hope this helped, Please let me know if you have any queries.
Patient replied :
Thank you so much I was thinking the same thing. Now it looks like I need to do the eliminating diet, since she is pretty much soly on breastmilk. The patches are still there just not inflamed. Would it be easier to do an allergy test since nothing in my diet is new?
An allergy test is not need at this stage. It need to be considered only if the symptoms persists for long period. Moreover the allergy test will only test for selected allergens and most likely will be inconclusive.
These lesions should resolve by itself in most cases. If not food (milk) it could be some minor viral infections , clothes, pollens (could be anything actually). So try removing any stuff you have introduced recently. Remember many a times a cause could not be found. And as I said earlier it is mostly self limiting.