Tears supply oxygen and nutrition to the cornea and help provide a smooth eye surface. A tearing eye may be a nuisance but usually is not a serious problem. Many people produce extra tears on cold or windy days. This is normal.
Tears:
Excessive tearing in one or both eyes includes tearing that is:
Excessive tears may indicate a problem with eye irritation or drainage of the tears. If irritation is causing the extra tears, the cause of the irritation needs to be identified and treated. Drainage problems can be caused by problems with the position of the lower eyelid or by a block in the drainage (tear duct) system.
Allergies may cause the eyes to produce an excessive amount of tears.
Some people with dry eye syndrome (keratoconjunctivitis sicca) complain of tearing too much. Actually, the eye becomes irritated because it does not make enough tears. This irritation causes more tears to be produced.
WebMD Medical Reference from Healthwise