Robin Dunbar, emeritus professor of evolutionary psychology at Oxford University, states that laughter, along with raising and lowering the eyebrows to expel air from the lungs, activates the endorphin system in the brain. Dunbar added, "Endorphins make you relaxed and happy, and they seem to reduce cortisol, the hormone responsible for stress."
Endorphins also help release nitric oxide, which aids in relaxing tense muscles, thereby enhancing stress relief. Nitric oxide dilates blood vessels, explaining the role of laughter in lowering blood pressure.
Professor Sophie Scott, a neuroscientist at University College London, notes that a highly complex network of brain areas is likely activated during laughter. She adds, "But we clearly see that the hypothalamus is activated, and we know it plays a role in stress."
The hypothalamus controls the autonomic nervous system. Scott explains, "Once we laugh, we observe a decrease in levels of the fight or flight hormone, adrenaline."
A study from the University of Basel, Switzerland, in 2020 found that the more laughter experienced throughout the day, the less affected individuals are by stressful events.
While natural and spontaneous laughter has stronger effects, there is evidence that artificial laughter can reduce stress reactions, known as the 'facial feedback hypothesis'.
Dr. Natalie van der Wal, assistant professor at Delft University of Technology in the Netherlands, explains that the facial muscles involved in smiling and laughing send feedback to the brain, which then releases chemical messages, such as serotonin, that improve mood. This response is utilized in laughter therapy.
A review of studies on laughter therapy published in the journal Social Science and Medicine in 2019 found that 18 out of 19 studies showed a significant decrease in feelings of stress after experiencing laughter therapy.
A study by researchers in Germany and Canada in 2021 found that a single 30-minute session could reduce cortisol levels, according to the British Daily Mail.
