PROBLEM TO BE SOLVED: To provide a method of screening a material for which interaction with a keratin substance is predictable.SOLUTION: A comparison is made between a fluorescence intensity (I) of a solution (I) of a peptide in which amino acids constituting a keratin are joined, and a fluorescence intensity (II) of a solution (II) in which the solution (I) is further blended with a test material, so as to screen a material blended in a composition for treating a keratin substance.