What happens to your skin's blood vessels as you exercise?

As you exercise, your skin’s blood vessels widen. This widening, called vasodilation, increases blood flow near the skin’s surface and helps your body release excess heat.

Working muscles generate heat, so body temperature rises during physical activity. The brain’s hypothalamus helps regulate this change by signaling blood vessels in the skin to relax. More warm blood can then move from the body’s core toward the surface, where heat escapes through radiation, convection and sweat evaporation.

The effect is especially noticeable when exercising in hot conditions: flushed or reddened skin reflects increased surface blood flow. In cold weather, the body does the opposite and narrows these vessels, called vasoconstriction, to conserve heat. Sweating and widened vessels work together, but they are not the same process—sweat cools mainly as it evaporates, while vasodilation moves heat outward.

Blood vessels may narrow briefly during intense exercise as blood is prioritized for active muscles, but the overall skin-cooling response is widening once heat removal becomes necessary.