Compatibility Testing of Colored Cosmetics – A New Tool for Objective Testing Near Infrared Remission Spectroscopy (NIR‐RS)

Abstract

Previous methods for skin compatibility testing of colored cosmetics were limited by their ability to detect erythema reactions (reddening) underneath non‐transparent products. The objective of this study is to present a new spectroscopic method to quantify reddening of human skin in vivo below colored cosmetics (e.g. hair dye, lipstick, makeup). The skin compatibility of non‐transparent cosmetic products was determined by detection of a remission band in the near‐infrared spectral region.In this study a spectrophotometer with a short arc xenon lamp and a single monochromator on the excitation side as well as an emission monochromator with a near‐infrared photodiode (NIR photodiode) on the detection side was used. To induce an erythema reaction different test areas were treated with a 1 molar solution of ammonia. Afterwards they were colored with a permanent oxidative hair dye or lipstick. Before the coloring procedure, the baseline state of the test areas was documented by measuring the remission in the range from 1050 nm to 1250 nm. This measurement was repeated after the erythema reaction had been covered by a colored cosmetic.The results of data analysis revealed a remission band at approximately 1150 nm that was directly linked to the intensity of the erythema reaction. Non‐visible reddening of the skin thus becomes measurable with this new method regardless of the optical properties of the product tested.