If your puppy is scratches itself a lot, it means it may be allergic to some kind food or have any other kind of allergy. The premium quality hypoallergenic food is an ideal food for the Chihuahua to keep it away from any kind of allergy. Fish, lamb along with potatoes or rice is the best food for the puppy.
If the food alternation is not able to eliminate the puppy’s allergy then the reason of allergy is something else. It may be because of any detergent, etc. It is better to consult any expert veterinarian to examine the skin.