Shunt, wrapped in muscleOxygen-rich bloodNerve keeping shunts shutFingertips, palms and toes have a shortcut in their skin: coiled shunts (arteriovenous anastomoses) that join small arteries straight to the veins under the surface, skipping the capillaries. Each is wrapped in muscle, and a nerve keeps it squeezed shut most of the time.In a hot flash the brain's heat-loss centre releases that squeeze. The shunts open, warm blood floods the veins just under the skin, and the finger's skin temperature rises about 2.7 °C within a minute while the heart beats about 10 beats a minute faster. The flash itself lasts a few minutes, but the finger stays warm for about half an hour.Typical values from laboratory recordings of women with hot flashes; the size of the rise varies widely (1–7 °C). Time runs fast after minute 7. Drawn far larger than life and simplified: real skin has many more shunts and loops.