From the manufacturer's website:
Pataday® is the first once daily eye allergy itch relief drop that’s available without a prescription. A single drop of Pataday® Once Daily Relief works directly on the cells that make your eyes itch. It’s fast relief that lasts all day.
How Does Pataday® Work?
Pataday® works two ways. It goes to work on mast cells in the eye. (Mast cells house the histamines that make your eyes itch.) Pataday® stabilizes the mast cells, preventing them from releasing histamines. Pataday® also blocks histamines that have already been released from attaching to the histamine (H1) receptors in the eye, breaking the chain of allergic reaction. Less histamines means less allergy eye itch.
Warning: See attached picture.
*These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease.