Infiltration of subcutaneous adipose layer into the dermal layer with aging

BACKGROUND: The elasticity of the dermal layer decreases with aging, leading to ulcer formation and wrinkling, but the mechanism of this change is not fully understood, because it is difficult to access the complex three‐dimensional (3D) internal structure of the dermis. OBJECTIVE: To clarify age‐dependent changes in the overall 3D structure of the dermal layer by means of 3D analysis technology. METHODS: We observed sun‐protected human skin by means of X‐ray micro CT, identified the layers of the skin, and reconstructed the 3D structure on computer. Age‐dependent structural changes of the dermal layer were evaluated by statistical comparison of young and aged skin. RESULTS: Histological observations suggested the presence of two types of ectopic fat deposits, namely infiltrated subcutaneous fat and isolated fat, in the lower region of the reticular dermal layer in aged skin. To elucidate their nature, we observed skin specimens by X‐ray microCT. The epidermis, dermal layer, and subcutaneous adipose layer were well differentiated on CT images, and 3D skin was digitally reconstructed on computer. This method clearly showed that the isolated fat observed histologically was in fact connected to the subcutaneous fat, namely all ectopic fat is connected to the subcutaneous adipose layer. Statistical analysis showed that the severity of fat infiltration into dermal layer is significantly increased in aged skin compared with young skin. CONCLUSION: Our findings indicate that subcutaneous fat infiltrates into the dermal layer of aged skin. Our 3D analysis approach is advantageous to understand changes of complex internal skin structures with aging.