Skin whitening
Skin-whitening efficacy was quantified by means of the melanin index using a Mexameter® MX18 (Courage + Khazaka Electronic GmbH, Cologne, Germany). Whitening efficacy was tested in the cheekbone area. The melanin index recorded was the average of three readings. The measurement is based on the absorption principle.10,11 The probe emits light of three defined wavelengths and a receiver measures the light reflected by the skin and thus the light absorbed. The melanin is measured by using two of the three wavelengths, which are chosen to correspond to the different rates of light absorption by the melanin pigments.