The skin under the eyes is very thin and does not produce as much of the protective oils that keep skin soft and supple. Under-eye gels are aimed at reducing puffiness and dark circles.
They typically work in one of two ways:
Temporarily constricting blood vessels to prevent the build-up of fluids.
Firming the skin with an invisible film.
Never rub under the eyes, as this may cause more wrinkles to form. Instead, apply these products with a light tapping motion to stimulate the skin.