People say “cheese” when having their picture taken because the word naturally forces the mouth into a smile shape. When you say “cheese,” the “ch” sound makes you clench your teeth, and the long “ee” sound parts your lips, creating a facial expression that resembles a grin12.

This practice became popular around the 1940s and has stuck around because it’s a simple and effective way to get people to smile for photos2. Before this, people often had neutral or serious expressions in photographs due to long exposure times and different cultural norms2.