The reason why the wrinkle suddenly becomes prominent at a middle age is addressed from biomechanical standpoint. The multistage buckling theory we have derived concludes that the sudden enlargement of wrinkle comes from a switch of the specific buckling mode from the horny buckling to the epidermal buckling. In this study, the validity of this conclusion was reexamined by the finite element buckling analysis of the human facial skin with a linear aging model. Comparison of results between the

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... eam model and the finite element model unraveled the mechanism of the buckling mode switch. By simulating the three cases: epidermal aging, dermal aging, and full aging, we found that the mode switch mainly comes from the epidermal aging, that is, the stiffening and thinning of the epidermis. The dermal aging was not a trigger of the mode switch in the linear buckling of linear aging skin model.