Disease is a term used to describe conditions that disrupt the delicate physiological balance (homeostasis) of the body. It is a disruption that often causes symptoms that can be measured. The disorder may be caused by viruses, bacteria, fungi, protozoa or aberrant proteins known as prions. Disease can be inherited or acquired. Acquired means that the condition began at some point after birth, as opposed to being present at birth, which is called congenital.
Some diseases have their origins completely unknown, which is referred to as idiopathic disease. As medical science advances, a few of these diseases will have their cause revealed and lose their idiopathic status, such as when germs are discovered to be the cause of an infection.
Other diseases are triggered by a particular environment or event, and these are considered to be infectious. Viruses, bacteria, fungi, or protozoa are the most common disease-causing organisms.
Sometimes risk factors that lead to disease – such as high blood pressure – become a disease in their own right, and the target range or threshold for the condition shifts over time. It is important to consider if the change in definition of a disease is warranted, as well as who benefits and whether there are conflicts of interest. For example, defining a physiological process like the menopause as a disease could have significant financial implications for healthcare. The new diagnosis may also impact the social expectations of the individuals involved.
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