Disease is the term used to describe any abnormal condition that affects the body’s ability to function. It is usually associated with a disruption of the delicate physiological balance (homeostasis) among chemical, physical and functional processes that control normal body functions.
Disease can be caused by many things, including infection with viruses, bacteria, fungi and parasites; chemical exposures; radiation, drugs or chemicals; and genetic abnormalities. Some diseases are more serious than others, and can be fatal.
Most human disease is the result of a combination of unfavourable exchanges with the external environment and unfortunate evolutionary legacies. However, the vast majority of diseases are not clearly attributable to any of these factors.
Noninfectious diseases are illnesses that are not caused by germs, such as cancer, diabetes and heart disease. You can get these diseases from your family, from the food you eat, or from living in an unhealthy environment. You can also develop them because of your genes or from aging.
A symptom is something that you feel or see that indicates that your health is not as good as it could be. A sign is an objective quality that can be noticed by someone other than the affected person, such as a fever, rash or swelling. The concept of disease is at the core of medicine, health care and public policy. It is an extremely complex subject, and different interpretations of the definition are often influenced by cultural contexts.