Health psychology is the 'use of psychological principles to promote health and to prevent illness' (Taylor, 1990). In other words, health psychology uses the knowledge and ideas from psychology to cut down on health risk factors, and promote healthy behaviors. Health risk factors include things like stress, overeating, and putting yourself in danger, including, for instance, not buckling one's seat belt, habits that increase chances of contracting illnesses. Being over-stressed is in fact a health risk factor, because stress can cause psychosomatic illnesses. Health promoting behaviors are any behavior that promotes health, and include things like good exercise, little stress, buckling seat belts, wearing a helmet, and healthy eating. Using health psychology by cutting down on health risk factors and increasing healthy behaviors can greatly increase ones chances of living longer.

Sources

Taylor, S. E. (1990). Health psychology. American Psychologist, 45(1), 40-50. Dennis Coon (1998). Introduction to psychology: exploration and application. Publisher: Brooks/Cole Publishing Company. Pages 450-453.