I would like to shed some light here on allergies for this discussion - for those of you who have posted that your dogs have allergies, you have discussed the triggers (food, environment, fleas etc.) but I have not seen any discussion of understanding the CAUSE of allergies. I hope this helps....
Allergies are the result of a hyper-sensitive immune system and tend to be genetically pre-disposed - the immune system is central to genetics but it can also be caused by immune system damage. Dogs with compromised or hyper-sensitive immune systems are usually those that have been assaulted by chemicals and unnatural preservatives (vaccines, flea/tick chemicals, pesticides and fertilizers, heartworm chemicals, chemically preserved dog food etc.) or whose recent ancestors have and have it passed onto to them in their memory T-cells. Studies show that it takes 3-4 generations to undue genetic or DNA damage from these items.
Ok..so back to allergies....y ou can focus on the triggers so long as you can reduce exposure to them or eliminate them for the animal's comfort, but the real focus should be on improving the immune system and vital force (or health) of the animal. To start, one must recognize that the worst thing you can do is pile on to the immune problem by injecting the animal with an immune suppressant (cortisone shots) - this is the ultimate failing of western vet medicine and should be well publicized for what it is - it creates an instant "impression" for us humans of help or health because it suppresses the immune system so far that it cannot react to the offense, thereby rendering it weak and ineffective for any purpose - including all the other things the immune system needs to protect against and in the future. We see a lack of external reaction and feel good - the animal is not in better shape, as the issue has just been driven down into the body further and will find another way out - eventually - either as more reaction, often worse and bigger than before - or a different reaction - such as hotspots, or goopy eyes, or gunky ears etc. Just remember that medically the skin is referred to as the "third kidney" due to it function as an expelling organ - the skin is highly effective at this function and will expel toxins and inpurities from our bodies when needed - our knee jerk reaction to want to suppress that and drive it back down is misguided - we need to let it out and this is why when humans get hives, most good doctors advise letting it "run its course through the body" until it is done expelling. Same for hotspots and other skin inflammation.
I have seen many things dramatically improve the condition and health of allergic prone dogs - to really get a great understanding of everything you can do, I highly recommend a book by a renowned holistic vet in the U.S., Dr. Martin Goldstein called "The Nature of Animal Healing" - He discussed allergies at length and other skin inflammation and gives a lot of help in his book. One product he recommends and so do I is called Beta-Thym - you can order it online - it contains plant sterols, contained in plant/veggies but deficient in our foods today and these help to modulate the immune system (or calm in down) - it also contains amino acids and thymus which both help to regulate the immune system and this product works well. Another thing I have found it allergies cannot truly be helped without a dramatic change in diet in most cases - the quality of food must be improved and if possible, fresh whole foods with enzymes, amino acids, vitamins and minerals intact should be provided - this always has a big impact and is what an immune deficient animal is lacking the most. It is critical that enzymes, amino acids et al be intact for nutrional absorption and therefore should not be destroyed by heat processing etc. Finally, remove the chemical assaults on the animal - an allergy dog is showing you the current state of the immune system and potential things to come in the future as a result. A continuous assault of flea, tick, heartworm, vaccine, and pesticides will result in cancer, kidney or liver disease eventually. By the way, vaccine manufacturers clearly print on their packaging for vets that a sick or compromised animal should never be vaccinated - they know this to be harmful and do not warrant their product if given to such an animal - a compromised animal includes allergies or other immune response (after all, this is the very system the vaccine is targeting) - so if your vet is advising vaccines knowingly for a highly allergic dog, time to find a new vet - mine would never do such a thing.
Sorry for this being so long - but hoping I explained this all - please pick up a copy of Goldstein's book, order some Beta-Thym, evaluate all the chemicals your pet is exposed to and eliminate, and research further to understand the importance of a wholesome diet for your dog.