A disease is a specific aberrant state that has a negative impact on the structure or function of all or part of an organism. It is not caused by an external harm. Different medical illnesses, which have distinct indications and symptoms are commonly referred to as diseases. External influences, like infections, or internal dysfunctions can both be a cause for a disease. Internal immune system dysfunctions, can result in a wide range of diseases, including immunodeficiency, hypersensitivity, allergies, and autoimmune disorders.
In humans, disease refers to any condition that causes discomfort, dysfunction, distress, social problems, or death to the individual afflicted, as well as equivalent problems for those who come into contact with the person. In this larger meaning, it may include injuries, impairments, disorders, syndromes, infections, isolated symptoms, deviant behaviours, and abnormal structural and functional alterations, albeit these may be regarded distinct categories in other contexts and for different purposes. Diseases effect people not only physically, but also mentally. As contracting and living with a sickness can change a person’s outlook on life and the perspective as well.
Natural causes refer to death caused by sickness. Infectious diseases, deficient diseases, hereditary diseases (including genetic and non-genetic hereditary disorders), and physiological diseases are the four basic types of disease. Diseases can also be divided into communicable and non-communicable diseases.
Coronary artery disease (blood flow obstruction) is the most lethal disease in humans. It is followed by cerebrovascular disease and lower respiratory infections. Neuropsychiatric disorders, such as depression and anxiety, are the diseases that cause the most sickness in affluent countries.
Pathology is the study of illness, which includes the study of aetiology, or cause.