The Scientist: Susan Stuart, M.D., a dermatologist in La Jolla, California
Hot water is the most effective at stripping oils from your hands, so—good as it feels when you’ve just come in from outside—doctors recommend that you not crank up the heat when you wash your hands. Stick to lukewarm water instead. Not only does a hot hand washing damage the lipid barrier on your skin, it also dilates the blood vessels just below the surface. When these capillaries open, more blood flows to the area, exacerbating fluid loss. On the flipside of the faucet, cold water constricts blood vessels, shunting blood and moisture away from the skin surface. Whether it’s by wearing gloves outside or settling for tepid water when you come back in, shielding your skin from extreme temperature changes is the best way to keep hands hydrated and soft.