Much of the volume of eyelids comes from water, fat and collagen. Skins losses its elasticity and becomes very dry. As the eyelid thins as a result of excessive water loss, the dark-blue blood vessels below the eyelid surface become more apparent, causing your eyelids to look dark and sullen.
Dehydration is just a medical term to describe people who has excessive loss of their body fluid. That is to say, the body does not have as much as water and fluids as it should. If your body lack of water, your body can't go on as normal. If you have a very severe dehydration, It will cause extremely sleepiness, seizures, sunken fontanel in infants as well as sunken eyes. So, drink more water everyday is good to keep healthy body.
There are many reasons that can cause sunken eyes, and dehydration is one of them, and you know what, dehydration is a condition that our body loss fluids, and most of it is water, exceeds the amount that our body take in. When we lose too much water, our bodies may become out of balance or dehydration, and one of the symptoms of dehydration in adults is sunken eyes, and you may want drink a lot of water, feel weakness or dizziness, and you'd better see the doctor if you are the dehydrated person.
When your body lacks water, it will look not spiritual at the skin. Actually the skin will intense, with no elastic character. For the eyes, the structure may shrink. That is why the dehydration causes the sunken eyes. You'd better eat the food with vitamin C to moisture the eyes.