[[File:Mycobacterium tuberculosis.jpg|thumb|upright=1.36|[[Scanning electron micrograph]] of ''[[Mycobacterium tuberculosis]]'', a [[bacteria|bacterium]] that causes [[tuberculosis]]]]
A '''disease''' is a particularan abnormal condition that negatively affects the [[structure]] or [[function (biology)|function]] of all or part of an organism, and that is not due to any immediate external injury.<ref name=":1">{{DorlandsDict|three/000030493|Disease}}</ref><ref>{{cite web |first = Tim |last = White |url = https://tgb.com.au/injured-people/what-is-the-difference-between-an-%E2%80%9Cinjury%E2%80%9D-and-%E2%80%9Cdisease%E2%80%9D-for-commonwealth-injury-claims/ |date = 19 December 2014 |title = What is the Difference Between an 'Injury' and 'Disease' for Commonwealth Injury Claims? |publisher = Tindall Gask Bentley |access-date = 6 November 2017 |url-status=live |archive-url = https://web.archive.org/web/20171027024609/https://tgb.com.au/injured-people/what-is-the-difference-between-an-%e2%80%9cinjury%e2%80%9d-and-%e2%80%9cdisease%e2%80%9d-for-commonwealth-injury-claims/ |archive-date = 27 October 2017 |df = dmy-all }}</ref> Diseases are often known to be '''medical conditions''' that are associated with specific [[signs and symptoms]]. A disease may be caused by external factors such as [[pathogen]]s or by internal dysfunctions. For example, internal dysfunctions of the [[immune system]] can produce a variety of different diseases, including various forms of [[immunodeficiency]], [[hypersensitivity]], [[allergy|allergies]] and [[autoimmune disorders]].
In humans, ''disease'' is often used more broadly to refer to any condition that causes [[pain]], [[Abnormality (behavior)|dysfunction]], [[distress (medicine)|distress]], [[social problems]], or [[death]] to the person afflicted, or similar problems for those in contact with the person. In this broader sense, it sometimes includes [[injury|injuries]], [[disability|disabilities]], [[Disease#Disorder|disorders]], [[syndrome]]s, [[infection]]s, isolated [[symptom]]s, deviant [[behavior]]s, and atypical [[human variability|variations]] of structure and function, while in other contexts and for other purposes these may be considered distinguishable categories. Diseases can affect people not only physically, but also mentally, as contracting and living with a disease can alter the affected person's perspective on life.
