Our Skin Is Covered With Invisible Stripes

Think the tiger and zebra have cornered the market on stripes? Think again — humans also have stripes, we just don’t see them. Human skin is overlaid with what dermatologists call “Blaschko’s Lines” — a pattern of stripes covering the body from head to toe. The stripes run up and down our arms and legs and hug our torso. They wrap around the back of our head like a speed skater’s aerodynamic hood and across our face. The reason we don’t see them is because they can only be seen under UV light. In the early 1900s, German dermatologist Alfred Blaschko reported that many of his patients had rashes and moles that seemed to follow similar formations, almost as though they were tracing invisible lines. Those lines, however, didn’t follow nerves or blood vessels and didn’t represent any known body system. Today, we know what they are: cellular relics of our development from a single cell to a fully formed human. Each one of us began as a single cell, then a little glob of cells. As the cells divided, some became muscles, others bones, still others organs, and some became skin. As those skin cells kept dividing, they expanded and stretched to cover a quickly growing body. One cell line pushed and swirled through another like steamed milk poured into an espresso to make a latte. Blaschko’s lines are the molecular evidence of those swirls (see photo below). Most people will never see their own stripes, and maybe that’s a good thing.
Blaschko's Lines seen under a UV light