The meaning of illness is individualized to each person who experiences an alteration in health. In contrast, disease is a medical term indicating a pathological change in the structure and function of the body or mind. It is a condition that has specific symptoms and boundaries.

An illness is a response to a disease in which the person's level of functioning is changed compared with a previous level. The general classification of illness includes acute and chronic.

Acute illness is severe and has a short duration. The symptoms appear abruptly, are intense, and often subside after a relatively brief period. Chronic illness usually lasts longer than six months. In addition, the individual may experience severe relapses that could be fatal and periods of maximum functionality with the characteristic remission and exacerbation.

Illness behavior involves how an individual monitors their body, describes and interprets their symptoms to take curative action, and uses the healthcare system. The stages of illness behavior include:

• Symptoms experience
• Assumption of the sick role
• Medical care contact
• Dependent client role
• Recovery and rehabilitation

Symptoms Experience

During this stage, a person identifies physical limitations or sensations but does not suspect a particular diagnosis. This stage involves physical, cognitive, and emotional aspects, such as a person's perception of pain, lump, or anxiety.

Assumption of Sick Role

Here, the person accepts the sick role if symptoms continue and become severe. At this point, the illness becomes a social phenomenon, and the person seeks confirmation from their family and social group regarding their symptoms.

Medical Care Contact

At this stage, the person seeks advice from health professionals to validate illness, explain symptoms, reassure, or predict the outcome and treatment.

Dependent Patient Role

The person relies on healthcare professionals to ease symptoms and adopt the dependent role in a healthcare institution, home, or community setting. The person must also adjust to the disruption of a daily schedule.

Recovery/Rehabilitation

During this stage, the person is free from the dependent role and resumes former roles and responsibilities. Recovery duration in acute illness is generally short and rapid, so it is relatively easy to return to their former lifestyle. In contrast, recovery time in long-term illness is long and more complex, which requires therapy to learn to make significant adjustments in functioning.