The Scientist: Susan Stuart, M.D., a dermatologist in La Jolla, California
The Answer: Though it may seem like a more effective way to wash your hands, scrubbing up with hot water doesn’t do your skin any favors, especially during the brutal winter months. Because cold air doesn’t hold humidity well, it’s very dry and leaches moisture out of your skin—especially those parts that are most often exposed to the elements, namely your face and hands. Your skin has natural oils that help create a barrier to keep moisture in. This is its main line of defense against the drying cold air outside, not to mention the just-as-dry hot air pumping in through the heating system at home and at work. When you wash your hands, you can wash away protective oils along with the dirt and germs you’re actually trying to get rid of. This leaves the moisture in your skin unguarded, allowing water to evaporate away and leaving your skin parched and susceptible to cracking.
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.