Do your eyes ever sting, burn, or feel scratchy? To be comfortable, your eyes need to be bathed, or lubricated, with tears. Normally, there is always a film of tears on the surface of your eyes. But if your eyes don't make enough tears or the tears are of poor quality, the surface gets irritated. This is called dry eyes.

When you cry, get something in your eye, or have an infection, your eyes make reflex tears. Each time you blink, another kind of tears (lubricating tears), spread over the surface of your eyes. These tears keep the eyes moist and comfortable. You aren't aware of these tears because they stay on the surface of your eyes.

Without lubricating tears, your eyes get dry. Then they burn or sting and feel scratchy. They may also water. But this doesn't ease the dryness. That's because the eyes water with reflex tears, not lubricating tears.

• Aging
• Heaters and air conditioners
• Wind, smoke, or dry weather
• Allergies, such as hay fever
• Medicines
• Eyelid problems, injuries to the eye, or diseases, such as Parkinson, lupus, or rheumatoid arthritis
• Eye surgery, such as LASIK
• Contact lens use
• Diabetes
• Vitamin A deficiency (rare in the U.S.)

Lubricating tears flow from glands in your upper eyelid over the surface of your eye. From your eye, the tears drain into small openings (puncta). These connect to drainage canals that lead to your nose.