But it became clear in the 1980s, through the pioneering work of social psychologist James Pennebaker, just how powerful a tool expressive writing can be in helping people work through challenges in their lives and improve their mental health.

Pennebaker was studying the body’s physiological response to stress when he stumbled upon the polygraph confession effect. Many polygraphers were making the same observation — even when faced with severe consequences, individuals felt relief after confessing their actions. Pennebaker became interested in exploring how keeping secrets contributes to physical illness. He came to the conclusion that people who experience trauma and keep it a secret, are more likely to have health problems. These ideas led him to launch his expressive writing studies.

Pennebaker and his team conducted sessions in which they instructed participants, in an experimental group, to write about past traumas expressing their deepest thoughts and feelings about the traumatic events. He simultaneously ran a control group in which those participants were asked to write about neutral topics, without any reference to their emotions and feelings. Both groups wrote for fifteen minutes every day for four days. In the writing group, the participants were shocked initially at being asked to write about their trauma. They had never been asked to reflect on these experiences before and many reported being upset by the experience, leaving the writing rooms in tears. But they kept returning and on the final day of the study, most reported that their participation had been valuable and meaningful for them. Pennebaker and his team tracked a number of measurements before and after the experiments.