They’re called Blaschko’s lines, after the dermatologist who first discovered them, Alfred Blaschko. It turns out that our skin cells arrange themselves on our bodies in a series of swirling stripes. However, since our skin cells are usually the same color it’s hard to notice. People with certain medical conditions that cause skin cells to be different colors can have visible Blaschko’s lines. They can often only be seen with ultraviolet light.
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