Schematic representation of main 3D skin model techniques. A To reconstruct human epidermis (RHE), keratinocytes can be seeded either onto an inert filter support or on a cell-free matrix/support. B To obtain human FTS with both a dermal and an epidermal equivalent, the matrix/support is populated with fibroblasts. In both models (A, B), the differentiation of the keratinocytes is promoted by cultivation at ALI. This step triggers the three-dimensional stratification of keratinocytes in multiple layers. In the most perfected models, the cornification process can be completed, resulting in skin or epidermis equivalents with all epidermis layers, including a well-defined cornified layer at their surface.