Beauty sleep is not a myth and sleep does lessen the severity of wrinkles on the face and neck, at least temporarily. Part of this is due to a decline in body temperature and a shift in body position. Every evening the body cools in anticipation of bedtime (about half a degree) and to do so, the circulatory system increases blood flow to the skin. This is why the cheeks often flush at night. In addition to this, early in the nightime sleep cycle, people typically have a surge in growth hormone. This period of deep sleep contributes to what people call "beauty sleep" as secretion of growth hormone helps repair and rebuild body tissues like muscle and bone. Many of the body's cells also show increased production and reduced breakdown of proteins during deep sleep. Since proteins are the building blocks needed for cell growth and for repair of damage from factors like stress and ultraviolet rays, deep sleep may truly be “beauty sleep”.