This post is pretty old, so I am not sure if anyone will read this. I have an allergic dog and it is NOT food allergies. If you can solve your dog’s allergies by diet then you are lucky. I have struggled with my dog allergies for years and I can offer some helpful advice. Also, I just had to put my dog back on steroids after several years and I can say the side effect are bad (the reason I came here). Anyway, I found a pretty good solution to manage my dogs allergies. You need to give the dog a bath every week using Ketochlor shampoo followed by a hydrocortisol shampoo. I put a video up on YouTube about it that nobody watches. Search for “Solution for itchy dog Nutfork”. I really hope this can help you! Dog allergies are really frustrating!
Corticosteroids have been used as drug treatment for some time. Lewis Sarett of Merck & Co. was the first to synthesize cortisone, using a complicated 36-step process that started with deoxycholic acid, which was extracted from ox bile .  The low efficiency of converting deoxycholic acid into cortisone led to a cost of US $200 per gram. Russell Marker , at Syntex , discovered a much cheaper and more convenient starting material, diosgenin from wild Mexican yams . His conversion of diosgenin into progesterone by a four-step process now known as Marker degradation was an important step in mass production of all steroidal hormones, including cortisone and chemicals used in hormonal contraception .  In 1952, . Peterson and . Murray of Upjohn developed a process that used Rhizopus mold to oxidize progesterone into a compound that was readily converted to cortisone.  The ability to cheaply synthesize large quantities of cortisone from the diosgenin in yams resulted in a rapid drop in price to US $6 per gram, falling to $ per gram by 1980. Percy Julian's research also aided progress in the field.  The exact nature of cortisone's anti-inflammatory action remained a mystery for years after, however, until the leukocyte adhesion cascade and the role of phospholipase A2 in the production of prostaglandins and leukotrienes was fully understood in the early 1980s.
Treatment is easy enough for this type of dog allergy ..... simply remove the item from your Schnauzer's environment. But that is more easily said than done.
Since your dog can't tell you what's causing the reaction, you will have to try and determine that on your own. Try keeping a journal of your dog's activities. This way when you see your dog scratching excessively you will know what he was doing just prior to the reaction. A bit of detective work on your part will help figure out what item(s) are the culprits.