This guidance describes the concepts of sameness, similarity, or difference in Q3 attributes of topical products and describes specific product characterizations that can be used to demonstrate the sameness, similarity, or difference in Q3 attributes between test topical products and reference standards for topical products. These concepts (and relevant product characterizations)can apply to a drug product that is a solution for application to the skin (e.g., characterization of physicochemical properties like pH), and are particularly useful when comparing test topical 111 products and reference standards for topical semisolid products