Neurotransmitters called endorphins are released when you smile.
Endorphins are triggered by the movements of the muscles in your face and are responsible for making us feel happy, and they also help lower stress levels. Faking a smile or laugh works as well as the real thing—the brain doesn’t differentiate between real or fake;
it relates to the face muscles. This is known as the facial feedback hypothesis.
Laughing expands the lungs, stretches the muscles in the body and stimulates homeostasis.
Laughing exercises the body, replenishes the cells and is the equivalent of a sit up; abdominal muscles contract and endorphin levels increase.