Huffpost Health Living February 6, 2013
Speaking of pillows, your sleeping position can also put a crimp in your complexion. "If you sleep on your side or front, rather than your back, it's like you're folding over your skin -- except it's sustained pressure," says Dr. Schultz. "It's breaking the collagen, which can give you wrinkles and make your skin look saggy." Sleeping on your back helps prevent fine lines from being etched into your skin overnight. But if you can't sleep prone, try sleeping on silk or satiny pillowcases instead, which are more forgiving and won't tug at your skin, causing fine lines.

American Academy of Dermatology (AAD)

The American Academy of Dermatology (AAD) cautions that sleeping in certain positions night after night leads to "sleep lines" -- wrinkles that become etched into the surface of the skin and don't disappear once you're up. Sleeping on your side increases wrinkles on cheeks and chin, while sleeping face-down gives you a furrowed brow. To reduce wrinkle formation, the AAD says, sleep on your back. Read More!

Web MD - How Sleeping Positions May Cause Wrinkles
The way your sleep may actually cause wrinkles. No matter how soft your pillow. it puts pressure on your face each night. Over years, this can etch lines into your chin, cheeks or forehead. Your personal pattern of sleep lines depends of how you tend to rest your face on the pillow. Read More!

Article Alley
Something that many people do not think about causing premature aging is the way they sleep. It is true-sleeping positions can cause wrinkles. For instance, if you sleep with your face resting on the pillow in the same way for many years, your can get wrinkles called, "sleep lines." Most of us have woken in the morning with a "line" across our face from the way we were sleeping. A "sleep line" is essentially, a permanent wrinkle. The best sleeping position is flat on your back - where your face cannot be scrunched up to create wrinkles. Read More! - Sleeping Positions
Resting your face on the pillow in the same way every night for years on end also leads to wrinkles. Called sleep lines, these wrinkles eventually become etched on the surface of the skin and no longer disappear when the head is not resting on the pillow. Women, who tend to sleep on their sides, are most likely to see these lines appear on their chin and cheeks. Men tend to notice these lines on the forehead since they usually sleep with the face pressed face down on the pillow. Read More!