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.
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. 
Molecules from one group differ sufficiently from other groups to explain the lack of cross-reactions among groups A, B & D. However, Budesonide which belongs to Group B is well known to cross-react with Group D steroids . Therefore, Budesonide is a marker for Group B and some of Group D steroids, like hydrocortisone butyrate (locoid). Molecular structure is not the whole story since cross-reaction patterns differ from patient to patient. Also, because of metabolism and degradation, several different molecules can be formed, resulting from reactions from the degradation product and not the parent compound. Because of the difficulty of predicting cross reactions, when hypersensitivity to one steroid is demonstrated all the steroids available in New Zealand should be tested, in order to recommend a valid alternative.