A method of identifying one or more single-nucleotide polymorphisms, SNPs, that influence the efficacy of one or a combination of ingredients within a cosmetic and/or skin care product and which can be used to test for product suitability for users. The method comprises identifying one or a combination of genes associated with one or more biological pathways which in turn are influenced the one or combination of ingredients. For the or each gene, SNPs that can be present within said gene(s) are identified, and the identified SNPs are rated to identify the SNP or SNPs that have a significant impact on the ability of the one or more biological pathways to be influenced by the ingredient(s).
