An effectiveness evaluating method evaluates effectiveness of an external preparation for skin for protection against ultraviolet irradiation after the external preparation is applied to the skin. The method includes a measurement step of measuring an amount of urocanic acid in a horny cell layer by Raman spectroscopy both before and after the application of the external preparation and both before and after exposure to ultraviolet irradiation, an index derivation step of computing at least one index for evaluating the effectiveness of the external preparation based on results of the measurement obtained in the measurement step, and an evaluation step of evaluating the effectiveness of the external preparation by using the index obtained in the index derivation step.
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