“I have dermatographia, a condition in which one’s immune system releases excessive amounts of histamine, causing capillaries to dilate and welts to appear (lasting about thirty minutes) when the hypersensitive skin’s surface is lightly scratched. This allows me to painlessly draw on my skin with just enough time to photograph the results. Even though I can direct this ephemeral response by drawing on it, the reaction is involuntary, much like the uncontrollable nature of a blush.”