Allergies - Dogs can be allergic just as humans can, to certain foods (wheat, soy, corn, preservatives, even meats, chicken, eggs, etc.), to plants, to insect bites (fleas, ticks, etc.), dust mites and molds to name a few. If the allergy affects the skin itching can be most severe on the feet, flanks, groin, armpits and earflaps. Products high in Omega 3 and 6 fatty acids may reduce inflammation.
My German Shepherd was bitten by an insect (we couldn't determine which one) at two different times and her muzzle and lips blew up to twice their size. The vet treated her with prednisone which worked very quickly. I keep prednisone tablets on hand now in case of another occurrence.
If you suspect or know that your dog has allergies, it's a good idea to keep medicine handy. Just check regularly to make sure the medication is not outdated.
There are commercial holistic pet foods (see Our Natural Pets) you can try. If allergies persist you can give your dog a home-cooked diet starting with a good quality meat and sweet potato or brown rice. If this works, you can gradually add other vegetables, oils and eggs, etc. one at a time until you can tell which food is causing an allergy.
Consult with your vet as to tests that can determine what your dog is allergic to.