Hi Ms. Coffman,   Allergic eye problems usually don't affect one eye. Contact allergy would be an exception though. Environmental (aerosol) allergens almost always cause both eyes to water and itch.   I require several answers to questions, and a look at yor child's eye to make a diagnosis. One tearing eye may be caused by:   -a tear duct problem (blockage or abnormal development) -foreign body perhaps under the lid or stuck on the eye -infection -inflammation from inverted eyelashes or infected roots of the eyelashes -scratched cornea -other possibilities   Recommendation: Take your child to your doctor for an evaluation. An eye doctor may be necessary if your primary doctor has difficulty with the diagnosis or treatment. Take your child in as soon as you can.   Best to you,   J. Thompson, MD