The complex geometry of our skin cells

Recently I’ve been trying to find face mites by sticking some clear tape on my forehead and cheeks. I still haven’t found one yet (I should probably stick the tape on my face longer) but what I do find consistently are these dead skin cells:

dead skin cells at 140x magnification

At first, I never paid much attention on them as I was determined to find face mites. But as I failed to catch a glimpse on those little critters over and over, eventually I noticed the peculiarity of the shapes of my skin cells. I also noticed that when the cells get caught on the tape, they are stuck together like tiles as they once did on my face, and rarely do I see a cell occurring alone. If these were living cells (like those found at the level of the stratum spinosum), then I wouldn’t wonder why they would still stick together. But these are dead skin cells (specifically, at the stratum corneum layer), and I don’t expect them to retain such mosaic-like integrity when they desquamate. Yet through foldscoping, I found out that somehow, they still do.

That’s when I thought that perhaps, their shape played a role in preserving such integrity. I began researching on the shape of our skin cells, and I found out that their shape resembles a very complex 3D structure called tetrakaidecahedron – a polyhedron with 14 faces – albeit sporting a more flattened version of it.

Upon further reading, I learned that in 1887, Lord Kelvin favored this shape over all other polyhedrons as “the best shape for packing equal-sized objects together to fill space with minimal surface area”. Furthermore, this shape contributes to the efficacy of our skin as a barrier to prevent leaks, as its multiple rectangular and hexagonal sides provide much areas for tight junctions to form barriers. Perhaps this is the reason how our skin cells maintain such strong “bonds” with each other even after they’re technically dead.

To examine this intricate arrangement among our skin cells more closely, I took more magnified pictures of my dead skin cells with the aid of the foldscope. I picked the clearest image that shows the cells packed together and digitally edited it with a white/blue phone camera filter to reveal areas that are more elevated than the background (represented by whiter areas). I then compared it with online images of how flattened tetrakaidecahedra would look like on top view when they are stacked on top of one another (i.e., specific arrangements when the tetrakaidecahedra would look more hexagonal, pentagonal, or quadrilateral on top view). Finally, I attempted to approximate the arrangement I observed and reconstruct it in 2D and 3D renderings.

Through this exercise, I found out that the surface of our skin is hardly ever completely flat, especially when working with this kind of shape. I also noticed that there are areas with faster cell turnovers (i.e., thinner areas) than other spots while being very close to each other, even if literature tells us that our skin cells follow a more organized system of layer-by-layer turnover. I’m not exactly sure why, but perhaps the layer of dead skin cells just work that way, while living skin cells still maintain an organized system as they are displaced upward to the surface. I’m also aware that there are some skin conditions like psoriasis where layers of skin cells pile up faster than these cells could desquamate, creating irregular turnover rates and producing very uneven skin surface, though I think (and hope) I’m not developing a skin condition anytime soon! I also think that some parameters as simple as the speed of tape removal from my skin or the current season or weather condition (like for instance, it’s summer here in the Philippines at present) could be at play as well. Who knows, maybe these are the same reasons why I still can’t find those face mites!

Here are more pictures of my dead skin cells collected from my forehead and cheeks:

References:

http://soft-matter.seas.harvard.edu/index.php/Tetrakaidecahedron_(Kelvin_Cell)

https://elifesciences.org/articles/19593

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