Despite what some have said, an allergy could be excema in a localized patch. My dd had it. Different parts of the body/organs etc have different IgE recepters. 50% of excema is food allergy related. Eliminate what food you think it is. It may take a while to go away. Reintroduce for 3 days (2x a day). It may be what's in the food or cross contamination with the food product (allergen on same production line or facility). Does she nurse? Could be something you're eating if it's allergic.
Trust your gut. We saw ped for her 1 excema patch. Dr. said it was nothing. Turned into various dots/pimples on her face...that changed daily. Happened for months. Dr. said it was nothing. Saw dermatologist, dr said it was nothing. Saw allergist...same response. She had dairy, vomited (fluid/blood) 4 hrs (literally nonstop) until passing out almost. Ped said to try dairy again in month. Tried again, same response. Also full body hives w/ egg. Saw allergiest again, confirmed food allergies, but gave us no support, info or epi. Saw Children's dr and loved them! Support, info, treatment plan etc.
Do a search for my posts to find a lot of info on resources dr's etc. PM me if you want more info.
Dr. Kim at Children's (glenview annex) is amazing. www.kidswithfoodallergies.org is the best resource for info, support etc. www.foodallergy.org is premeire world wide org for FA"s w/ great info, tools etc.
Good luck! I hope it's not food, but if so, there's a lot of help out there.