Transdermal patches (adhesive patches placed on the skin) may also be used to deliver a steady dose through the skin and into the bloodstream. Testosterone-containing creams and gels that are applied daily to the skin are also available, but absorption is inefficient (roughly 10%, varying between individuals) and these treatments tend to be more expensive. Individuals who are especially physically active and/or bathe often may not be good candidates, since the medication can be washed off and may take up to six hours to be fully absorbed. There is also the risk that an intimate partner or child may come in contact with the application site and inadvertently dose himself or herself; children and women are highly sensitive to testosterone and can suffer unintended masculinization and health effects, even from small doses. Injection is the most common method used by individuals administering AAS for non-medical purposes. 
When asked what advice she would offer to other dog owners, Catherine suggests that owners never assume that their dog is allergic to just one thing. If the dog has allergies, they are usually allergic to several different elements. She also suggests that if dog owners decide to use Prednisone, they should go with the lowest dosage available and look into giving them milk thistle to prevent against liver damage. Owners should be open to trying new medications and therapies and never give up. It’s important to try everything they can to keep their pup as comfortable as possible.
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.