Each individual reacts to physical illness in her or his unique way. Some overcome it with courage and others have difficulty in overcoming intense emotions like anger, fear, or hopelessness. Various factors affect the response of an individual to an illness and its effect on the illness, for example, denial as a response to an illness may result in delay in seeking treatment. Medical and paramedical personnel working with the patients having chronic physical illnesses should understand their patients’ reactions towards their illnesses. It will help to plan the treatment, modulate the patients’ behavioural or emotional responses, decrease their distress and improve their medical outcomes. In this Unit we try to view illness as stress and the individual’s psychological, emotional and behavioural response to the illness. 
6.1 DEFINITION of CHRONIC ILLNESS
The term chronic comes from the Greek word chromos; it means lasting for a long time. Examples of common chronic illnesses include asthma, epilepsy, cancer, diabetes, heart disease and chronic fatigue syndrome. United States National Center for Health Statistics (NCHS) defines a chronic illness as one lasting three months or more. The Commission on Chronic Illness (1956) defines chronic illness as: 
“All impairments or deviations from normal which have one or more of the following characteristics: are permanent, leave residual disability, are caused by non-reversible pathological alteration, require special training of the patient for rehabilitation, and/or may be expected to require a long period of supervision, observation or care.”
Chronic illnesses can begin at any time in life from childhood to old age and can create long-term health concerns that require adjustments in normal living. Chronic illnesses may differ in treatment, severity and prognosis. They may lead to disability (visible/invisible or static/progressive) thereby impairing the quality of life. In the life of the patients, their families and others who care for them (for example the whole family is affected when the primary wage earner is the patient), modifications need to be made.