A disease is any abnormal condition of the body or mind that causes discomfort, dysfunction, or distress to the person affected or those in contact with the person. Sometimes the term is used broadly to include injuries, disabilities, syndromes, symptoms, deviant behaviors, and atypical variations of structure and function, while in other contexts these may be considered distinguishable categories.
Illness can be another term used for disease or it can be a person's perception of their health without regard to having a disease. A person without any disease may feel unhealthy and believe he has an illness. Another person may feel healthy and believe he does not have an illness even though he may have dangerously high blood pressure which may lead to a fatal heart attack or stroke.
Older medical usage sometimes distinguished a disease, which has a known specific cause or causes (called its etiology), from a syndrome, which is a collection of signs and/or symptoms that occur together. This pedantic distinction has become less valid as the causes of many conditions have been identified, yet they continue to be referred to as "syndromes". Furthermore, numerous conditions of unknown etiology are referred to as "diseases" in many contexts.
A condition can be objectively verifiable, but considering it a disease is a social value judgement. For example, in current North American society the number of people considering shortness and obesity as diseases to be treated has been increasing over the last 40 years, and the number of people who consider homosexuality to be a disease has been decreasing.
A condition may be considered a disease in some cultures or eras but not in others. Oppositional-defiant disorder, attention-deficit hyperactivity disorder, and sociopathic personality disorder are examples of conditions considered diseases in current North American society but not recognized in American culture a century ago or in many other cultures currently.
Sometimes whether a condition should be considered a disease or a variation of human structure or function becomes an intensely political controversy because of significant social or economic implications. For example recognition of post-traumatic stress disorder, also known as shell shock, were highly politicized processes in the United States, as was repetitive motion injury in Australia.
One of the largest and best-known categories of disease, infectious diseases are those caused by transmissible infectious agents such as bacteria, fungi, parasites, viruses, and prions. Closely related though not infectious diseases in the strictest sense are parasitic diseases caused by protozoa and worms. There are also genetic diseases caused by the presence or absence of genes in the affected person's DNA; toxic diseases caused by exposure to environmental toxins such as heavy metals; nutritional diseases caused by lack or deficiency in certain nutrients; conditions caused by injury, malformation, or disuse of parts of the body; autoimmune diseases caused by immune system attacks on the body's own tissue; diseases caused by the patient's own beliefs; and diseases caused by combinations of these, and of course totally unknown causes.
- Infectious diseases
- Genetic diseases
- Conditions of injury, malformation, or disuse
- Autoimmune disorders
- Toxic diseases
- argyria, alcoholic hepatitis, iron poisoning, lead poisoning, ...
- Nutritional diseases
- Endocrine diseases
- Syndromes and diseases of unknown etiology, or of mixed causes
- Neurological disorders and mental illnesses
- Psychogenic illness
- multiple chemical sensitivity, mass sociogenic illness
The World Health Organization publishes a comprehensive list of diseases known as International Statistical Classification of Diseases and Related Health Problems (ICD). It was originally designed as a tool for describing diseases from a public health perspective. In the United States the ICD9 code list has been primarily used for insurance and billing purposes and is widely considered obsolete and incomplete.
In biology, disease refers to any abnormal condition of an organism that impairs function.
The term "disease" is often used metaphorically for disordered, dysfunctional, or distressing conditions of other things, as in disease of society.
- List of childhood diseases
- List of common diseases
- List of diseases for a huge list of 6000+ diseases, many very rare.
- Center for Disease Control Health Topics A-Z, fact sheets about many common diseases
- The Merck Manual, detailed description of most diseases, freely searchable online.
- Health Topics, MedlinePlus descriptions of most diseases, with access to current research articles.
- International Classification of Diseases (one long page)
- Cultural, philosophical, and social dimensions of the concept of disease