Why Do People Get 'Bags' Under Their Eyes?

As any sleep-deprived person with a mirror knows, dark circles under the eyes are usually prominent after a bad night's sleep.

But why do people get these dark, purplish eye bags in the first place? The answer is both genetic (that is, relating to your DNA) and environmental (a result of your everyday living, such as rubbing your eyes or getting too little sleep), said Dr. Carol Clinton, a skin-care specialist at Timeless Skin Solutions in Dublin, Ohio.
But "genetics is the biggest culprit," Clinton told Live Science.
Eye bags are generally more noticeable in people who, because of genetics, have thin or pale skin. That's because a fair complexion does little to hide what's going on behind the scenes of the face. When people are tired or stressed, blood circulation in the eye area tends to slow, allowing blood to pool there, Clinton said. Capillaries (thin blood vessels) stretch and leak, leading to puffy, dark eye circles, she said.  
Moreover, some people are genetically prone to subluxation, the movement of fat from underneath the eyeball to the front of the eye. (It's worth noting that a 2008 study published in the journal Plastic and Reconstructive Surgery suggested that eye bags develop not from existing fat moving forward, but rather from an age-associated increase in fat beneath the eyeballs.)
Either way, "when you have the fat moving forward, that's when people think about having surgery in that area," Clinton said. She added that subluxation is not related to how much sleep a person gets. In other words, a person can get 9 hours of sleep a night, but still have eye bags because of a genetic predisposition, Clinton said.
In other cases, environmental factors cause puffy eye bags. For instance, allergies — especially seasonal allergies — can cause capillaries to leak, Clinton said. When the body is exposed to allergens, it releases immune proteins known as histamines. These substances can cause blood vessels in and around the eyes to swell, she said.
Getting too much sun can also damage and thin the skin, making dark circles under the eyes more visible, Clinton said. Moreover, eating salty foods can cause the body to retain more water, exacerbating eye bags, according to the Mayo Clinic.
In addition, rubbing your eyes can also cause dark circles, because this action stimulates capillaries that are already prone to leaking. To avoid the urge to rub your eyes, try putting an ice cube on your closed eyes for 60 to 90 seconds when they feel itchy, Clinton said.
"The cold compress is going to constrict the blood vessel, and it will stop the itching sensation," Clinton said. "You'll notice immediate relief."
Sometimes environmental factors beyond a person's control, including gravity, can cause eye bags. As people age, they lose collagen (a structural protein) and elastin (an elastic protein) found in connective tissue. The bones in the face also lose volume as people age, so "everything just hangs" off of the face, and that contributes to eye bags too, Clinton said.

SOURCE:
LiveScience