Dr. Oz's Beauty Book

Before diagnosing Crystal, Dr. Oz explains what causes acne.

Hair grows from a deep follicle where it also has a blood supply. "And sometimes the sebum, the oil that normally coats our skin, comes out from down below and is supposed to come out of this hole," he says. "But if you overgrow this, you clog it and then this stuff builds up and becomes pus."

That pus increases, raising the skin and becomes a pimple.

Now, if you're thinking about popping a zit, Dr. Oz says to think twice—especially if it's in the triangle from the tip of your nose to the edges of your lips. "This is called the triangle of death," he says. "When you squeeze a pimple in here, that pus doesn't have to come up. Instead of the pus going [out], it can go back down into those blood vessels. And guess where they go? They go to your brain."

There are other cosmetic dangers too. "You can actually cause more scarring, more damage," Dr. Evans says. "In some cases, you get a dark spot there."