| Abstract: | Background: Most studies on wrinkle formation have focused on changes in the dermal condition that promote the fixation of transiently formed wrinkles. Little is known about the age‐dependent changes in transient wrinkle formation in response to altered facial expression or the mechanism leading to fixed wrinkle formation. Objective: To clarify the mechanism of wrinkle formation at the forehead, we investigated the factors that influence the severity of transient wrinkling and the relationship of transient with fixed wrinkles, using a newly established method to evaluate transient wrinkle formation. Methods: Transient wrinkles were generated by requesting subjects to gaze in an upward direction. Foreheads of the subjects with or without an upward gaze at a fixed angle were photographed and the severity of wrinkles at the forehead was graded from 0 to 5 in 50 healthy Japanese female volunteers in their 20s, 40s, or 60s. Skin elasticity was measured using a Cutometer®. Frontalis muscle activity and ptosis of the upper eyelid were estimated by measuring movement of the eyebrow during upward gazing and the position of the upper eyelid of the open eye, respectively. Results: Wrinkles formed transiently at the forehead by upward gazing were highly reproducible in each subject. Their severity increased with aging and was highly correlated to that of fixed wrinkles (R=0.81, P<0.001). Therefore, this method appears to be suitable for studying the mechanism of transient wrinkle formation and the relationship between transient and fixed wrinkles at the forehead. The severity of transient wrinkles was correlated with elevation of the eyebrow during upward gazing (R=0.69, P<0.001), but not with dermal elasticity. This suggests that transient wrinkles are induced by increased frontalis muscle activity during upward gazing. Frontalis muscle activation was negatively correlated with upper eyelid position (R=?0.37, P<0.05), which descended with aging, meaning ptosis of the upper eyelid, and negatively correlated with the severity of transient wrinkles induced by upward gazing (R=?0.43, P<0.05). Furthermore, the upper eyelid position was also negatively correlated with the severity of fixed wrinkles (R=?0.44, P<0.05). Conclusion: These results suggest that ptosis of the upper eyelid is associated with increased activation of the frontalis muscle during upward gazing and increased severity of transient and fixed wrinkling at the forehead. |
