Turns out that glass of milk your mother may have forced you to drink as a kid may actually be harmful to your skin and health. Dr. Jessica Wu, M.D., Los Angeles-based dermatologist and author of "Feed Your Face" says cow's milk -- even organic -- contains its own hormones and growth factors that are absorbed into the bloodstream. These hormones have androgenic effects that can cause acne in women. Dairy products are also pro-inflammatory, which means they can worsen acne issues and also accelerate aging, says dermatologist Nicholas Perricone, M.D. So find your calcium in other forms, such as dark leafy greens and tofu.

Speaking of tofu and other protein-packed foods, it's a good idea to limit your consumption of protein and not consume more than one type at a time. "Protein takes the most digestive work, as the foods have to be broken down into amino acids from complex chains," says celebrity nutritionist Kimberly Snyder. This energy spent on digesting protein takes away from what Snyder calls your "Beauty Energy," which she describes as "energy that can be redirected away from digestion to grow thick, healthy hair, clear up dark under-eye circles, repair the collagen in our skin, etc."

Cortisone is one of those products in your home's first-aid kit that you most likely use to treat rashes and bug bites. While mild, over-the-counter forms like Cortaid and cortizone-10 can relieve redness, swelling, and flaking, it's easy to forget that cortisone is a type of steroid, and continual long-term use can lead to tachyphylaxis. That's medical speak for cortisone addiction, says Wu. "[When] the skin gets so used to having cortisone around to control any inflammation, it reacts if you suddenly stop using it," she says. "The skin 'rebounds' by becoming angrier and itchier than ever."

Overusing cortisone cream also causes collagen to break down, which leads to thinning of the skin and -- worst-case scenario -- stretch marks. So, how to use this product safely? Wu says to only use it when you really need it, and for a max of two weeks at a time. Also, use the mildest form and apply a very thin layer on areas with thin skin, such as the groin, face, and underarms.

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.