Sure, flushing post workout may be an annoying side effect of a hardcore workout for some, but the reason behind it is pretty cool. Allow board-certified dermatologist Hadley King, M.D., to explain.
“When you exercise, your body temperature increases. One of the homeostasis mechanisms used by the body when body temperature increases to maintain a healthy body temperature is to carry more blood to the surface of the skin, so that heat loss from the skin increases,” she says. “This entails peripheral vasodilation—or widening of the small blood vessels found in the skin so that more blood is carried through them. This can cause a red, flushed face, particularly noticeable in fairer skin types.”
Essentially: Working out causes improved circulation no matter who you are—a good thing that has a laundry list of benefits for the skin and body—but for these with skin that is extra transparent or even thin, the color comes through far more visibly.