As children, our mothers scrupulously scrubbed the dirt off our faces. Now that we're all grown up, we're paying good money to put it back on. Aestheticians, the ladies who give you those spa facials, love mud for its ability to absorb oil and exfoliate the skin. But not just any mud will do the trick. The best way to use mud in your beauty ritual, doctors say, is with a mask—just make sure you use a mud product that has been refined for cosmetic purposes with the tiny sharp particles ground smooth. And be aware that mud can be drying, so be careful when using it on delicate or sensitive skin.