When your eyes are exposed to allergy-causing substances, a substance called histamine is released by your body. The blood vessels in the conjunctiva become swollen. The eyes can become red, itchy, and teary very quickly.
The pollens that cause symptoms vary from person to person and from area to area. Tiny, hard-to-see pollens that may cause hay fever include grasses, ragweed and trees.
Your symptoms may be worse when there is more pollen in the air. Higher levels of pollen are more likely on hot, dry, windy days. On cool, damp, rainy days most pollen is washed to the ground.
Allergies tend to run in families. It is hard to know exactly how many people have allergies. Many conditions are often lumped under the term "allergy" even when they might not truly be an allergy.