Doctor's advice: Rinse with just water in the morning instead, and wash your face with cleanser at night. "Water is enough to clean your skin, and you'll retain more of the moisturizing oils," says Ellen Marmur, a cosmetic and dermatologic surgeon at Mount Sinai Medical Center.

Video: The secrets of beautiful skin >

If your skin can't take the heat, get out of the gym. High temperatures in fitness classes (Bikram yoga, Spinning, and Tracy Anderson) may trigger hyperpigmentation, especially in areas like the face that are already exposed to the sun, says Hema Sundaram, a Washington, D.C., dermatologist.

Doctor's advice: If you're prone to brown patches, consider vigorous alternatives like Ashtanga yoga and don't go into the sauna.

Video: How to avoid skin spots >

If acne's a problem, your pillowcases may be part of the cause. "They collect skin oil, dead skin cells, bacteria, and excess night creams," says Bank. "As you toss and turn, all of that is deposited right into your pores." Doctor's advice: Change your pillowcases at least once a week, but twice is better, says David Bank, a professor of dermatology at Columbia University/New York-Presbyterian Hospital.

Video: Beautiful Skin: A Simple Skin Care Routine >

Chronic lack of sleep triggers a chain reaction of events that reduces collagen production, cell turnover, and barrier repair. "Your skin looks duller and drier, and wrinkles will form more easily," says Howard Sobel, a clinical attending physician in dermatology at Lenox Hill Hospital in New York City.

Doctor's advice: A warm shower or bath raises the body's core temperature. When it begins to drop again, the hormone melatonin is released, making us sleepy, says psychologist and sleep medicine expert Michael Breus. Stay under the water for ten minutes. Since heat can dry out the skin, make sure to moisturize before you go to sleep.

Video: 7 Overnight Beauty Remedies >