Because of its involvement in the body's stress response, cortisol levels are among the most popular used to measure the presence and intensity of stress in various situations. Cortisol in itself is not harmful, and is in fact a vital part of the body's healthy functioning. However, during times of chronic stress, the body can experience elevated levels of cortisol, which can have negative short-term and long-term ramifications for health. (Read this for more on cortisol.)
Because of the damage that elevated cortisol levels and long-term stress can do, it's vital to have an effective stress management plan that includes multiple layers of stress relief strategies. Take advantage of these stress management resources for short-term and long-term stress management help, and see this resource for stress management basics.