Dermo-epidermal junction
The dermo-epidermal junction is the boundary between the epidermis and the dermis. Far from flat, it is folded into interlocking ridges that increase the contact area between the two layers and anchor them to each other.
The line between the epidermis and the dermis is the most consequential boundary in skin, and it is not a line at all.
It is folded. Projections of epidermis descend into the dermis and projections of dermis rise between them, interlocking like fingers. That folding is why the junction appears wavy on every cross-section of skin, including the schematic used throughout this site, and it is not decorative: the interlocking multiplies the contact area between the two layers and resists them being sheared apart.
Several things depend on it holding. The epidermis has no blood supply of its own and is nourished by diffusion across this boundary. When the junction separates, fluid gathers in the space, which is what a blister is.
Depth is assessed relative to it. Damage confined above heals without a mark, because the epidermis renews itself completely; damage passing below reaches tissue that does not rebuild identically, which is what scarring describes. A pathologist reporting on a sample says where a process sits in relation to this boundary, and that placement carries much of the meaning of the report.
It is also where a dermatoscope reveals most of what it reveals, which is why so much assessment of pigmented areas is really assessment at this depth.
Last updated .