In contrast with disease, which has some statistical basis, illness is the term given to a subjective feeling of unwellness. This can occur in the presence or absence of any biological deviation (“disease”) and it is largely what determines whether of not people consult a doctor and take medicines. It is complex, being influenced by a range of demographic and more complex psychosocial components, including role embeddedness (how well integrated a person is into his social group) and identity strength, social support, perceived control, work status, perceived threats, demands and resources, and personality characteristics. These are not things you’ll find in any anatomy or biochemistry text book and genome knowledge is little help.

Disease may be what people have, but illness is what drives them to seek help, even when they may not have a disease as such. In the biological model of disease, this difference in what is present and how people behave cannot be accommodated. However, in the systems model, illness is a flag for dysfunctioning at some level. Many doctors when confronted with illness look for disease. When this is found the disease is treated but the illness, which may or not be related to the disease, remains untreated. If no disease is found, the doctor often scolds the patient and may even accuse him of malingering or hypochondriasis, both of which are derogatory and morally judgmental terms. This generates great dissatisfaction in the patient.