• Product Application 3 The last product application should be performed the evening before the measurement (at least 12 h). Otherwise, a risk of measuring the Cosmetic remnants on the skin surface exists. When the protocol of the study does not allow a 12-h period free of product application, cleansing of the skin might be useful by a mild,nonalcoholic, and nonaggressive cleanser at least 2-3 h before the measurement.