A well-placed cucumber may feel wonderful, but there is no special ingredient in it that reduces swelling under the eyes.
Cucumbers are 90 percent water, and it is the cooling effect of the water that constricts the blood vessels around the eyes, therefore decreasing the swelling. The colder the cuke the better.
Some other swollen-eye solutions include black tea bags in cold water, the tannic acid content being the key to reducing swelling. Hemorrhoid cream also helps, but I’d prefer puffy eyes.
From the book “Why Do Men Have Nipples?”