RESUMEN
BACKGROUND: To investigate the intrinsic mechanism that causes the darkening of liquid foundations. MATERIALS AND METHOD: A total of 36 commercial liquid foundations were firstly studied for preliminary screening of influencing factors. A basic liquid foundation was developed for controlling variables to study the influence of each single factor. These samples were evenly spread on the standard opacity charts with the thickness of 100 µm and applied onto human inner forearm skin with the dosage of 2 mg/cm2 . The discoloration of each sample was continuously recorded using spectrophotometers and reported in the CIE 1976 L*a*b* color space for at least 120 min, and ΔE was calculated to describe the severity of darkening. RESULTS: One hundred twenty-minute ΔE of all commercial foundations was highly negatively correlated with their 120-min ΔITA° (R2 = 0.88, p < 0.01). A strong positive correlation was found between the severity of darkening and the volatilization of the basic foundations (R2 = 0.83, p < 0.01). And the darkening of silicone-based basic foundations using pigment coating with silicon is weaker than those without silicon (p < 0.05). CONCLUSION: The process of the discoloration of liquid foundation is accompanied by the decrease of ITA° and manifested as darkening. The volatilization rate of the product and the coating method of the pigments used in the formula can noticeably affect the darkening of the liquid foundation.