How does fatigue affect the skin?

While the importance of sleep has always been common knowledge, last year Ariana Huffington’s The Sleep Revolution caused a stir when she brought to our attention just how little rest the average person receives in today’s modern world.
As well as its impact on our mood, health, social and personal life, lack of sleep can also wreak havoc on our skin. In fact, a 2013 study found that the faces of sleep-deprived individuals were perceived as having darker circles, paler skin and more fine lines/wrinkles as well as an increased ‘droopiness’ around the corners of the mouth.
But just how is a lack of sleep causing these effects?