The tears that keep the eyes moist are produced by the conjuctiva, while the tears produced by crying come from the lachrymal glands located in the eyelids. According to Moment of Science, the chemical composition of tears from the lachrymal glands leads to puffiness in the eyelids.

The tears produced by crying are less salty than those that keep the eyes moist. Moment of Science explains that this additional water causes the water in the tears to migrate to the less salty tissue of the eyelids through a process called osmosis. The extra water in the eyelids causes the tissue to swell and become puffy.