Somehow we replace our entire outer layer of skin every two to four weeks, but it never leaks, and now scientists say they’ve figured out why – it’s made of a unique arrangement of shapes called tetrakaidecahedrons, which never leave a gap, even as individual cells are sloughed away.
“Our study is also helping us to see how the cells that make up our skin can switch on a mechanism to make a kind of glue, which binds the cells together, ensuring that our skin maintains its integrity,” says one of the team, Reiko Tanaka, from the Imperial College London.
While scientists have long been studying the outermost layer of the epidermis, which is constantly shedding dead skin cells and replacing them with newer, healthier ones, little is known about the thin, secondary skin barrier that sits beneath it, called the stratum granulosum.
The stratum granulosum is crucial to ensuring that our skin doesn’t leak, because it’s the layer where the tight junctions form, and the outermost layer of the skin could not form without them.
For mammals to shed their outer layer of skin, new skin cells must be continuously produced in the lowest layers of the epidermis, before they’re moved up into the stratum granulosum.
The team figured out that this shape allows the new skin cells to replace old cells by producing a protein that acts as a temporary ‘glue’, which holds both the old skin cell on top and the new skin cell beneath in tight junctions with those around them, so that even if the top cell is lost, the barrier stays intact.
The researchers say that corneocytes – a type of skin cell in the outermost layer of the epidermis – in humans are more variegated in humans than in mice, their tetrakaidecahedron model still applies, and this could make a big difference in research into human skin conditions.