Liquid allergen extracts contain proteins, such as (but not limited to) tree, weed, cat, cockroach, and nuts, and are used to identify allergies by observing the body's reaction to the introduction of extract underneath the skin. There are a few dog allergen extracts commercially available in the US for allergy testing; however, none of these products are standardized, meaning they are not required to be the same strength. Because some extracts are not as potent (strong) as others, it's possible that some patients' allergies are misdiagnosed. Typically, the most potent (strong), but safe extract should be used so that allergic patients are correctly diagnosed.