Under eye bags is the puffiness or swelling that is sometimes seen under the eyes, as one gets older. The swelling could be due to fluid (water) or it could be due to fat. Essentially the cause is due to the loss of elasticity in the tissue around the eyes creating a potential pouch for the accumulation of the fat or fluid. When an otherwise healthy younger person presents with this condition, it is safe to assume that it probably runs in the family or there is a poor sleep history attached. A sudden acute puffiness with itching and redness could be due to some dermatitis or allergy and would require a different approach to treatment.