Hyaluronic acid stays in the eye longer than other humectants (producing a long-lasting effect) and significantly increases tear break-up time.
It has viscoelastic properties. When the eye is open, the tear is resistant and unlikely to break (viscous) but becomes fluid when the eye is closed (elastic).
Hyaluronic acid is a biological molecule that is found naturally in the eye tissue. This means the eye tolerates it extremely well and there is no chance of reactions.