When a person cries for a longer period, the tears tend to get warmer, as revealed by a new study.
A new model of the fluid dynamics and heat flow in human tears has been created by mathematicians from the University of Delaware in the US.
When people blink their eyes - the formation point of a tear - a thin liquid film is spread across the surface of the eye.
The surface of the tear film then cools slightly, and for dry-eyed patients the rate of cooling can be higher.
But the Delaware researchers have established that the temperature of the tear film actually increases slightly between each blink, the Daily Express reported.
So if copious tears are produced they are warmer.
Tears are produced not just by emotional distress but also by other circumstances, which cause eye irritation, for instance peeling onions or inhaling pepper dust.
Future work by the team will seek better ways to model tears during the motion of a blinking eyelid.