Cortisol is a corticosteroid hormone or glucocorticoid produced by the adrenal glands. It is usually referred to as the "stress hormone" because it is involved in response to stress and anxiety. Its primary function is to increase blood sugar and storage of sugar in the liver as glycogen. It also suppresses the immune system. Various synthetic forms of cortisol are used to treat a variety of different illnesses. The most well-known of these is a natural metabolic intermediary of cortisol called hydrocortisone - a natural anti-inflammatory.

Cortisol levels rise and fall as a response to stress. In the absence of stressors, cortisol levels in the blood follow a "diurnal variation". This means that cortisol is mostly active during the daylight hours. Our levels are highest when we arise and they gradually decline throughout the day to their lowest levels at bedtime.

Here are a few of the actions cortisol is responsible for;

Stress is everywhere. Both negative and positive stressors can lead to stress. Some common categories and examples of stressors include: sensory input such as pain, bright light, or environmental issues such as a lack of control over environmental circumstances, such as food, housing, health, freedom, or mobility.

Social issues can also cause stress, such as struggles with nonspecific or difficult individuals and social defeat, or relationship conflict, deception, or break ups, and major events such as birth and deaths, marriage, and divorce.

Life experiences such as poverty, unemployment, depression, obsessive compulsive disorder, heavy drinking, or insufficient sleep can also cause stress. Students and workers may face stress from exams, project deadlines, and group projects.

Adverse experiences during development (e.g. prenatal exposure to maternal stress, poor attachment histories, sexual abuse) are thought to contribute to deficits in the maturity of an individual's stress response systems.