Watery or teary eyes occur when the body produces tears too quickly. There is usually an equilibrium between tear production and tear loss, but outside influences such as bright sun and high winds can cause tears to evaporate, disrupting the balance and causing watery eyes. Various eye disturbances, internal or external, also can upset this equilibrium and lead to excessively watery eyes. For instance, various airborne allergens can lead to high levels of tear production, as can foreign objects or eyelashes in the eye. Additionally, highly emotional situations can lead to crying, another condition in which the eyes produce tears at a higher rate than necessary.
Allergies, particularly to various airborne allergens, such as mold, dust, dander, or pollen, are among the most prominent causes of watery eyes. Tiny particles of these allergens get into the eyes, causing them to water and, in many cases, to become red and itchy or otherwise irritated. Sometimes, the wind may blow larger particles, such as a plant fragment or eyelash, into one's eye; this also causes watery eyes, which often last until the object can be removed. It also is possible for such objects to cause tiny cuts or abrasions on the eyes, often leading to long-term watering and discomfort.
In some cases, watery eyes can be caused by environmental factors unrelated to allergens or particles. Wind, cold, or intense sunlight can also cause watery eyes. Wind and sun, in particular, can increase the rate at which tears evaporate. The eyes then water at an increased rate to maintain eye moisture.
Another common cause of watery, teary eyes is a condition known as dry eye. The eyes of individuals with this condition do not produce basal tears — the normal tears that are constantly produced for lubrication purposes — at a fast enough rate. The dry eyes, then, are not as well lubricated and can become more easily irritated than well-lubricated eyes. Irritation triggers the production of "reflex tears" such as those produced in response to dust, allergens, or weather conditions. Individuals with dry eye, then, may experience long, uncomfortable periods of dryness in the eyes followed by irritation and excessive watering.
Eyes generally water in order to expel some irritant, so treatment of watery eyes is seldom aimed at actually stopping the watering. It is, instead, aimed at preventing irritation in the first place. Various allergy medications can decrease irritation from allergens and therefore reduce watery eyes. Eye drops can keep dry eyes lubricated, thereby making irritation less likely and preventing excessive tearing.