Illness (sometimes referred to as ill-health or ail) can be defined as a state of poor health.

It is sometimes considered a synonym for disease. Others maintain that fine distinctions exist. Some have described illness as the subjective perception by a patient of an objectively defined disease.

Introduction

The mode of being healthy includes, as defined by the World Health Organization, " 1 a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity". When these conditions are not fulfilled, then one can be considered to have an illness or be ill. Medication and the science of pharmacology is used to cure or reduce symptoms of an illness or medical conditions. Developmental disability is a term used to describe severe, life-long disabilities attributable to mental and/or physical impairments.

Physical

Conditions of the body or mind that cause pain, dysfunction, or distress to the person afflicted or those in contact with the person can be deemed an illness. Sometimes the term is used broadly to include injuries, disabilities, syndromes, infections, symptoms, deviant behaviors, and atypical variations of structure and function, while in other contexts these may be considered distinguishable categories. A pathogen or infectious agent is a biological agent that causes disease or illness to its host. A passenger virus is a virus that simply hitchhikes in the body of a person or infects the body without causing symptoms, illness or disease. Foodborne illness or food poisoning is any illness resulting from the consumption of food contaminated with pathogenic bacteria, toxins, viruses, prions or parasites.

Mental

Mental illness (or Emotional disability, Cognitive dysfunction) is a broad generic label for a category of illnesses that may include affective or emotional instability, behavioral dysregulation, and/or cognitive dysfunction or impairment. Specific illnesses known as mental illnesses include major depression, generalized anxiety disorder, schizophrenia, and attention deficit hyperactivity disorder, to name a few. Mental illness can be of biological (e.g., anatomical, chemical, or genetic) or psychological (e.g., trauma or conflict) origin. It can impact one's ability to work or go to school and contribute to problems in relationships. Other generic names for mental illness include “mental disorder”, “psychiatric disorder”, “psychological disorder”, “abnormal psychology”, “emotional disability”, “emotional problems”, or “behavior problem”. The term insanity is used technically as a legal term. Brain damage may occur