"Dehydration is one of the top causes of puffy eyes," says Day. "Not having enough water in your system shifts the water from inside to outside your cells, causing puffiness. To reduce under-eye bags you have to drink water."

The amount of water to drink, she says, depends on your weight and activity level. A safe bet is between half-an-ounce to an ounce of water for each pound you weigh. If you're doing a rigorous workout, you may need more. Drinking water also helps flush inflammation-causing salts from your tissue, which you can get from eating too much sodium. (Another good rule of thumb: Avoid salty foods.)

No matter how bad your allergies or how drowsy you feel, resist the urge to rub your eyes. Eye rubbing causes inflammation, says Day, which can make under-eye skin appear swollen.

Use eye drops, such as Visine's lubricated Tired Eye Relief Eye Drops, $8.99, to keep over-worked eyes from feeling fatigued. If your eyes are itchy, you could have an allergy you're not aware of. The American College of Allergy, Asthma and Immunology estimates that 50 million people in the US have seasonal allergies -- that's 30 percent of all adults. Does this sound like you? Ask your doctor about antihistamine eye drops, specially formulated to treat eye-itching due to allergies.

Take a look at Mom and Dad. If they have puffy eyes, chances are you've inherited the condition. Unfortunately topical creams won't do much to get rid of bags under your eyes, but you do have a few choices for a long-term fix.

Blepharoplasty is a surgical procedure that removes extra fatty tissue and excessive skin from upper and lower eyelids and tightens skin and muscles to reduce puffiness and wrinkles. It costs around $3,000, depending on your location.

Another option is a carbon dioxide (CO₂) laser treatment to resurface the skin, which strengthens and thickens skin so the fat pad is less prevalent. Likewise, for hereditary pigmentation, such as under-eye circles, ask your dermatologist about CO₂ laser resurfacing, which has been shown to lighten skin.

Age ain't nothing but a number -- until we're talking puffy eyes. As you get older, your skin thins and sags, and muscles around your eyes weaken. Healthy fatty tissue that ordinarily protects the eye inside the bony eye socket can begin to move into the lower eyelids, causing them to appear puffy says Day. Fluids may also accumulate, she says.

Thankfully, there's a whole lot topical eye creams can do for puffy eyes. "Look for products that contain ingredients that make skin firmer, including niacin, vitamin C, retinol, caffeine and copper," she says. "They all have skin-firming properties and you want to make skin as firm as possible to counteract the puffiness."

We like L'Oréal Paris RevitaLift Triple Power Eye Treatment, $24.99, which uses caffeine to help reduce under-eye bags and lift the eye area. Then there's the Philosophy Ultimate Miracle Worker Eye Cream, $70, which contains vitamin C and caffeine. It promises to reduce the appearance of puffiness after two weeks use.

Life's a bit of a roller coaster -- and it can take its toll on your appearance. Lack of sleep, hangovers, stress and crying can all cause puffy eyes. Cold water, a cold compress, cold spoons (with the bowl of the spoons covering eyes) -- anything cool applied to exhausted, stressed, crying eyes will help constrict blood vessels and reduce swelling.

For an added boost, use chilled tea bags. Black tea contains caffeine that helps narrow blood veins, and green tea possesses powerful antioxidants that soothe under-eye bags. Steep two black or green tea bags in hot water and refrigerate overnight. In the morning, let the excess liquid drain off the tea bags and gently place each tea bag over closed eyes. Leave on for five minutes.

Another age-old remedy is to cover closed tired, puffy eyes with sliced, chilled cucumbers. Cucumbers contain antioxidants and flavonoids that are said to reduce swelling, redness and irritation. They contain caffeic acid, which constricts dilated blood vessels, thus reducing the appearance of the puffiness around the eyes. Try leaving 'em on your lids for 10 to 15 minutes.