The Involvement of Nitric Oxide in Skin Dullness Induced by Mechanical Stimulation

Dullness of the skin around the eyes is one of the most serious cosmetic problems. However, the causative mechanism of skin dullness, especially in the skin of the upper eyelids, remains unclear, and effective treatment needs to be established. The skin of the upper eyelids is particu-larly exposed to mechanical stimulation such as compression or friction by repetitive and multiple applications or removals of make-up. Mechanical stimulation has already been reported to induce hyperpigmentation of the skin. We hypothesized that dullness of the skin of the upper eyelids might be caused by melanin formation through mechanical stimulation. We conducted two ex-periments using reconstructed human skin models; the first experiment showed that repetitive loadings of weight resulted in the activation of melanogenesis, and the second one demonstrated that the activation of melanogenesis was inhibited by the addition of a nitric oxide scavenger. These results suggest that nitric oxide is involved in mechanical stimulation-induced melanogenesis. In addition, a skin lotion containing nitric oxide scavenging preparation, wasuregusa flower ferment filtrate, did not reduce the dullness of the skin of the cheeks, where the relative frequency of mechanical stimulation is low, but did reduce that of the upper eyelids. These results support our hypothesis that mechanical stimulation contributes to the dullness of the skin of the upper eyelids and suggest that nitric oxide plays an important role in mechanical stimulation-induced melanogenesis. Therefore, nitric oxide and its generation need to be targeted to reduce skin dullness.