Beauty sleep is not a myth and sleep does lessen the severity of wrinkles in the face and neck, at least temporarily. Part of this is due to a decline in body temperature and a shift in body position. The body cools in anticipation of bed time (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.
What does it mean to be “radiant”? It generally means the color of the skin moves closer to the color of blood. A radiator in a house or car movers hot liquid around to distribute heat, and so does the circulatory system move warm blood around and skin tone changes to affect body temperature. This is why some people appear more radiant just before bedtime or during sleep.
Early in the nightime sleep cycle, people typically have a surge in growth hormone. This period of deep sleep, stages 3 and 4 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 tissues also show increased cell production and slower 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 is truly be "beauty sleep."
Increased growth hormone release is believed to be linked to the fasting state that the body enters during sleep. Contrary to what bodybuilders might want to believe, injections of growth hormone are more effective at stimulating collagen formation than preventing muscle atrophy. This suggests that naturally occuring growth hormone also plays a big part in maintaining collagen matrix, and hence the appearance of youthfulness.
There is some evidence that skin cells regenerate faster at night than during the day. Cell division happens throughout the day, but peaks around 2 am. This is literally renewal and rejuvenation during sleep. The peak in cell division happens even if you stay awake at night, while the surge in growth hormone doesn't.
Human nighttime sleep is lengthy in comparison with that of many other mammals. Other animals usually don't have releases of growth hormone during sleep and few other mammals enter a fasting state during sleep. Herbivores continue to digest food throughout their sleep, carnivores gorge themselves on meat which can take up to a day to digest, and rodents wake up periodically to nibble more food. The human sleep-related growth hormone surge may be a mechanism to protect tissue protein against potentially decremental effects of this fast, and also to promote the body's mobilisation of its fat reserves.
What happens if you don't get your beauty sleep? It is not just lack of sleep that negatively affects body fat percentage and the risk of chronic disease—poor sleep quality does as well. Deep sleep also helps to negate the bad effects of cortisol. Growth hormone naturally decreases with age and also with increased abdominal fat, leading to a viscious cycle of fatigue, excess stress hormone and increased abdominal fat. It has also been found that sleep deprivartion causes breaks in "skin barrier function and mucous membranes". Researchers recently found apnea sufferrers who use their CPAP machines look younger and fresher than those who do not.
Activity in parts of the brain that control emotions, decision-making processes, and social interactions is drastically reduced during deep sleep, suggesting that this type of sleep may help people maintain optimal emotional and social functioning while they are awake. This is another benefit of beauty sleep.
Some cosmetic products are susceptible to sunlight and you consequently get more out of them if you use them before bed. Antioxidants such as vitamins C and E will stay active on your skin longer if you apply them at night. (Whether these products truly prevent aging is another question.)
Some people advocate sleeping on your back – as opposed to your side or stomach – in a belief that this position prevents wrinkles. A website produced by the American Academy of Dermatologists suggests that "resting your face on the pillow in the same way every night for years on end also leads to wrinkles." They suggest sleeping on your back to avoid wrinkles.
Sleep does lessen the severity of wrinkles in the neck and face, at least temporarily. Some smoothing is due to position - lying down diverts the force of gravity. But there's more to beauty sleep than that - otherwise just lying down to rest in the middle of the day would have the same effect. During sleep the whole body, including the face, perspires more. This moisture on the skin smooths out wrinkles. Some cosmetics make your face looks better by making the skin more moist. Sleep is a natural moisturizer - perspiration during sleep is a natural skin treatment.
Stress has detrimental effects on skin tone; it causes alopecia areata,
psoriasis, and atopic dematitis. Chronic stress harms the integrity of the collagen in skin. Sleep deprivation applies stress to the body and
leads to unhealthy appearance. Apnea causes much stress to not just the cardiovascular system, but has been shown to affect bone health.