Protection against singlet oxygen, the main actor of sebum squalene peroxidation during sun exposure, using Commiphora myrrha essential oil.

Squalene is a component of sebum. Both are directly exposed to the external environment and play a key role in skin physiology. They are particularly prone to photo oxidation during sun exposure. We studied the impact of two types of antioxidant on sebum squalene peroxidation by UV irradiation. The first type is free radical scavenger (Butyl hydroxyl toluene and an olive extract rich in hydroxytyrosol). The second type is the essential oil of Commipora myrrha, a singlet oxygen quencher. These properties were confirmed using the 2,2-diphenyl-1-picrylhydrazyl test for antiradical capacity [Yoshida et al. (1989) Chem. Pharm. Bull., 37, 1919; Buenger et al. (2006) Int. J. Cosmet. Sci., 28, 135] and 1,3-diphenylisobenzofuran test for the capacity to quench singlet oxygen [Kochewar and Redmond (2000) Meth. Enzymol., 28, 319; Racine and Auffray (2005) Fitoterapia, 76, 316]. Furthermore, we have extended an ex vivo method to classify the efficacy of cosmetics to protect squalene by collecting sebum in vivo and irradiating it in a controlled way. The squalene monohydroperoxide formation is monitored by high performance liquid chromatography. This methods allows us to compare the efficiency of the three antioxidants at 0.6% in a cosmetic formulation to protect squalene from photo oxidation. Our results clearly show that essential oil of Commiphora myrrha provides the best protection against squalene peroxidation. These results demonstrate that squalene peroxidation during solar exposure is mainly because of singlet oxygen and not due to free radical attack. This suggests that sun care cosmetics should make use not only of free radical scavengers but also of singlet oxygen quenchers.