The thing is that hair is a lot tougher than skin. So the same chemicals that destroy the hair can also cause serious skin irritation–and possibly even chemical burns–if left on too long.
Researchers agree that optimum napping time is between fifteen minutes and two hours. During a nap that’s shorter than fifteen minutes, you never enter the most restful phase of sleep. But if you sleep for over two hours, you might not be able to fall asleep when you turn in for the night.