Causes of swelling under the eyes include aging, fluid retention, lack of sleep, allergies or dermatitis, or genetics, according to Mayo Clinic. Bags underneath the eyes are not usually an indicator of a serious illness or injury.
Aging causes the tissue around the eyes to weaken, claims Mayo Clinic. This weakness, paired with fat that shifts into the lower eye space, causes a puffy appearance.
Chilled compresses improve the appearance of puffy eyes, and if allergies are the cause, allergy pills provide relief, as well. Getting adequate sleep and propping the head up on a pillow while sleeping prevent the appearance of under-eye puffiness, adds Mayo Clinic.