International of Cosmetic Science : Increase in subjective well-being and psychological health after application of C8-silk lipoamino acid functionalised pigments included in a foundation
The aim of this study was to evaluate the effects of two foundations before (D0) and after 5 days of application (D6) on psycho-physiological parameters in order to compare C8-silk lipoamino acid functionalised pigments (FA) versus pure pigments (FP).
Assessment of self-esteem, stress, mood, emotion using psychological tests and evaluation of salivary cortisol concentrations were realized on 40 healthy females using a crossover study design at D0 and D6. Four saliva samples were taken on the awakening (C1), 30 min after the awakening (during the foundation application (C2)), 1h after the foundation application (C3), and at 1900h (C4) at DO and D6. Area under the curve was calculated in order to obtain information about the total amount of a given substance excreted in a specific time period.
Five days of daily application of the foundation containing the pigments treated with the C8 silk lipoamino acids induced a significantly increased (P < 0.001) of self-esteem and Pleaseant Emotion (P < 0.05), and a significant decrease of General Stress (P < 0.05). This was not the case after the FP application. Cortisol concentrations presented a pronounced diurnal rhythm whatever the foundation used. At DO, no significant differences were observed between the groups. At D6, cortisol concentrations measured 30 min and 1h after the FA application were significantly lower (P < 0.05: C6.2, P < 0.05 C6.3, respectively) than those reported after FP application. AUC, a global stress response indicator, was significantly lower in FA group as compared to FP group after 5 days of application. Subjects found a decrease of tiredness signs, and thought that FA has a good coverage.
Our results show that incorporation of C8-silk lipoamino acid as agent of pigment functionalisation brings new benefits to a foundation. Adopting a psychophysiological approach, which are not invasive to the subjects, we show that the measurement of cortisol at the same time that psychological indicators provide a scientific approach to examine the beneficial effects of a cosmetic product.