In recent years, wellness influencers have become fixated on cortisol, blaming the stress hormone for various symptoms, including a puffy face and excess belly fat. Many suggest that high-intensity or prolonged aerobic exercise puts too much stress on your body and causes your cortisol level to spike in an unhealthy way.But scientists say this is a misunderstanding of cortisol’s role in the body. A surge in cortisol, they add, is not always bad, especially in response to exercise. We asked experts to explain the science around exercise and cortisol.CORTISOL IS ESSENTIAL TO GOOD HEALTHCortisol’s main role is to help your body respond to stress: When you are under strain, your adrenal glands release the hormone to help set off the so-called fight-or-flight response. Cortisol helps increase blood flow to your muscles and gives you a burst of energy by spurring your body to convert fast-acting carbohydrates to fuel.These responses would be essential if, say, you were being chased and needed to run away, said Dr Lena Fan, an endocrinologist and assistant professor at the Icahn School of Medicine at Mount Sinai. Cortisol also helps you fight off infection and inflammation, and helps regulate heart rate, blood pressure, blood sugar and sleep cycle.CORTISOL DISORDERS ARE UNCOMMON