A stressor is anything that causes the release of stress hormones. It can be an event or situation that causes stress, and just about anything can be a stressor as long as it is perceived as a danger. Stressors can be internal or external factors, like our memories, environment, or the people around us. There are two broad categories of stressors: physiological (or physical) stressors and psychological stressors.

Examples of physiological stressors include very cold/hot temperatures, injury, chronic illness, or pain. On the other hand, psychological stressors are events, situations, individuals, comments, or anything we interpret as negative or threatening. These can include not being able to find a babysitter for your sick child when you cannot take time off work, time pressure at work, traffic, paying taxes, writing an exam, societal and family demands, and more.

Stressors can cause physical, chemical, and mental responses internally. Physical stressors produce mechanical stresses on skin, bones, ligaments, tendons, muscles, and nerves that cause tissue deformation and (in extreme cases) tissue failure. Chemical stresses also produce biomechanical responses associated with metabolism and tissue repair. Psychological stressors can lead to anxiety, depression, and other mental health issues.

It is important to learn how to identify the sources of stress and how they impact us to address and mitigate them. Stressors can be further divided into absolute stressors and relative stressors. Absolute stressors are stressors that everyone exposed to them would interpret as being stressful, while relative stressors are subjective stressors that cause different reactions in different people.