This branch of psychology has only flourished fairly recently (i.e., the last 10-15 years) because of the importance of exercising and healthy eating. For the past one hundred years it was assumed that health and illness were biomedical issues. It was thought that a person's genetic makeup caused them to be ill or sick. Health was just considered to be the absence of disease. When medical research improved -- such as with modern surgical techniques and the use of medications, and immunizations -- it reduced death rates and helped to prevent many once life-threatening diseases. But, the chronic illnesses such as heart disease, cancer, lung diseases, and complications from substance abuse, continued to rise in the second half of the twentieth century.

It eventually became clear that many chronic illnesses could have been prevented or at least managed better through modifications in behavior. This is when interest in health psychology started to multiply. It was found that approximately 350,000 heart attack deaths could be prevented each year through the cessation of smoking alone. Other controllable behaviors, such as lack of exercise and poor diet, have also been found to contribute to the onset of chronic diseases. Health psychologists have found that not only behavior has an impact on disease, but also attitudes and social factors. These factors combined to form the biopsychosocial model which guides the work of many health psychologists today.