Can you explain how pollen makes your eyes itchy if you are allergic to it?

Histamine release. A person has allergies if his immune system over-reacts to certain types of pollen, and the histamine (and other chemicals) released by his immune system causes itching, runny nose, watery eyes, wheezing, cough, lots of mucus, etc... The treatment is avoidance of pollen, and use of oral or eye-drop antihistamines, and nasal steroids. For bad eye allergies, eye doctors prescribe eye-drop steroids.
Allergy. The simple explanation is that when you are allergic to pollen, your immune system is programmed to react to it when seen, releasing histamine. Histamine causes blood vessels to dilate leading to swelling and itching.

Related Questions

What allergy eye drops can I purchase to relieve itchy eyes due to the high pollen count during the summer?

Antihistamine. While lubricating drops help some, antihistamines drops do the most for eye allergy symptoms, including itching & watering. There are many over-the-counter antihistamine products to choose from. Older products may be combined with decongestants which decrease redness; however, overuse of these products may cause increased rebound redness. Plain antihistamine drops are your best bet for itching.
These work best. The best way to treat eye allergies is with pills recommended by your doctor. Adding prescription nasal sprays also works nicely. Adding over counter allaway or zaditor drops is first choice. Last resort, prescription drops such as Pataday or bepreve (bepotastine besilate). My patients have achieved control of eye allergies following this.