Table of contents

Part 1 - Theory: Thinking About Health

Chapter 1 Concepts of Health and Illness

Illness, Sickness, and Disease

Discussing the complexities of what constitutes a disease requires careful distinction among related, but distinct concepts. In 1973, Susser, an epidemiologist, proposed some definitions that remain useful.4 He used ‘illnessillnessthe subjective sense of feeling unwell that often motivates a patient to consult a physician.’ to refer to the subjective sense of feeling unwell; illness does not define a specific pathology, but refers to a person’s subjective experience of it, such as discomfort, tiredness, or general malaise. The way a patient reports symptoms is influenced by his or her cultural background, and Susser applied the term ‘sicknesssicknesssocially and culturally held conceptions of health conditions; these may influence how the patient reacts, as in the dread of cancer or the stigma of mental illness.’ to refer to socially and culturally held conceptions of health conditions (e.g., the dread of cancer or the stigma of mental illness), which in turn influence how the patient reacts (See CultureCulturethe coherent and characteristic set of beliefs, customs and values shared by, and characteristic of, a group, community or nation. These are transmitted from generation to generation but may evolve; they include the characteristic intellectual and artistic creations that characterise the group. in Glossary). The social perceptions of disease that Illich described modify the ways a patient perceives and presents his symptoms.2 Cultural conventions likewise affect where the boundary between disease and non-disease is placed: menopause may be considered a health issue in North America, but symptoms are far less commonly reported in Japan.5,6‘Disease’ implies a focus on pathological processes that may or may not produce symptoms and that result in a patient’s illness. For example, a patient complains of tiredness and malaise–his illness as he experiences it. He consults a doctor about it–because he believes that he might have a sickness. The doctor might attribute the patient’s symptoms to a thyroid condition–a disease.

The ‘biomedical model’ of disease has dominated medical thinking since the time of Louis Pasteur (1822–1895) and the microbiological revolution. This model focuses on pathological processes, and on understanding, diagnosing, and treating the physical and biological aspects of disease. The goal of treatment is to restore the patient’s physiological integrity and function. Diagnosis involves recognizing and applying a label to a pattern of signs and symptoms that is at least partly understood in terms of abnormal structure or function of cells, organs, and systems. This offers a rational basis for the investigation of effective treatments. For instance, a certain pattern of chest pain known as angina pectoris is understood biologically as a disorder of the coronary arteries that causes cardiac ischeamia, and the treatments it are geared to the specific causes of restoring cardiac blood flow and reducing cardiac effort.

Early biomedical conceptions supposed that a disease is either present or absent: a bacterium has invaded the body or it has not. However, as medicine increasingly tackled conditions, such as hypertension, which represent deviations from normal values, which themselves have a range and can be debated, it became apparent that there may be no set threshold for defining disease. Thus, instead of being seen as a state that is qualitatively distinct from health, many diseases have to be approached as a quantitative threshold on a continuum of biological variability (see Nerd’s Corner box on alternative definitions of disease). Organizations such as the World Health Organization (WHO) and the National Institutes of Health have proposed different classifications of hypertension and have changed how they constitute hypertension over time. Hypertension can be mild, moderate or severe, or defined as pre-hypertension or hypertension stage 1 or stage 2. Ways of establishing what is a ‘normal’ value is further discussed in Chapter 6.

Alternative Approaches to…

Alternative Approaches to Defining Disease

Basis for the definition of ‘disease’


It can be difficult to define what ‘pathological’ means, especially in cases of psychological or behavioural disorders. What is the threshold between ‘normal’ and ‘pathological’? This often leads to defining threshold in terms of impact on function: see below.

Abnormal conditions that lead to impaired or altered function

Implies that disease exists only when it impairs function. This further implies that, if the person does not complain, then it’s not worth bothering with. This may leave conditions such as slowly deteriorating eyesight in elderly people, untreated.

Illness or sickness that produces unpleasant symptoms

Use of alternative terms (‘illness’ or ‘sickness’) does not really help; again implies that disease must produce symptoms.

Questions to ponder:
If no symptoms are produced, is it a disease?
Are health and disease different entities or merely different points along a continuum?
If so, should we abandon the notion of disease and think only of different levels of health, changing from a categorical to a dimensional model?


Perhaps disease should be defined in terms of a pathological process (physical or mental) that, if left untreated, would naturally progress to producing symptoms and damaging function.

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