While we know we should wash our makeup brushes once a week (or at least once a month -- we know how unrealistic it is to give them a good scrub-down every week), Wu says a common mistake is not letting them breathe after washing them.

Need a good reason to take this extra, time-consuming step? "I had a patient who developed a rare skin infection normally seen in aquarium workers and those who work with fish," says Wu. "We traced it back to her makeup brush that she'd been using twice a day but never aired out [after washing]." The lesson: Wash your brushes and don't stash 'em until they're bone dry. And of course, see your doc if you develop a new rash.

While there are obvious health reasons to avoid recreational drugs, now there's another (disgusting) consequence that can result if you just say yes: You could find crusty, purplish areas of dead skin on your body that have a good chance of getting infected. Gross.

A recent study in the "Journal of the American Academy of Dermatology" found that patients with this rare disorder, Purpura, all had traces of levamisole in their blood -- a de-worming drug that was found in 70 percent of confiscated cocaine in 2009, according to the U.S. Drug Enforcement Administration.

"We believe these cases of skin reactions and illnesses linked to contaminated cocaine are just the tip of the iceberg in a looming public health problem posed by levamisole," say the study authors. While the de-wormer has been found in cocaine since 2003, drug enforcement officials have found its levels in recreational drugs have risen in recent years due to its efficacy as a diluting agent. As we learned during our elementary school days, the clear message here is don't do drugs. Especially if you don't want ugly, painful purple sores.

Be wary of miracle supplements that are sold over-the-counter and not recommended by your dermatologist or primary care physician, says Wu, as they can interfere with prescribed medications. For example, calcium supplements can reduce the efficacy of medications like antibiotics or thyroid hormone pills. And vitamin D supplements can make Lipitor (a cholesterol-lowering medicine) less effective.

Wu says, even if you're not on any meds, "mixing supplements can be hazardous to your health." For example, mixing omega-3 fish oil supplements with other supplements like ginger, gingko, or even Advil, can lead to an increased risk of bleeding, which is especially dangerous if you're undergoing surgery or even a teeth cleaning.

You've heard the eight glasses a day rule a trillion times, we know. But it turns out your body doesn't retain a lot of that water, since it goes right through you during your frequent bathroom breaks. The secret to retaining water is by eating it, says Dr. Howard Murad, M.D., founder of Murad, Inc. and author of "The Water Secret."

Murad suggests noshing on foods that have large quantities of H2O, such as watermelon (97 percent water) and zucchini (95 percent water). Cells can more easily absorb the water in food since it comes along with other nutrients that the body needs to absorb. As a general rule, start eating more fruits and vegetables, which have higher percentages of water than processed foods and meat.

Your dermatologist can prescribe medication for various skin ailments like acne and rosacea, and the prescription can be good for several months at a time. However, Wu says it's a good idea to see your derm again before you refill an Rx. "Some medications need to be monitored closely, such as isotretinoin (formerly known as Accutane)," she says. "[Others] can be harmful to your liver, drop your blood pressure, or cause electrolyte imbalances. I usually see my patients at least every couple of months, or even more frequently [if they're on] isotretinoin."