Disease

For example, internal dysfunctions of the immune system can produce a variety of different diseases, including various forms of immunodeficiency, hypersensitivity, allergies and autoimmune disorders.

The immune system is a host defense system comprising many biological structures and processes within an organism that protects against disease.

Diseases are often known to be medical conditions that are associated with specific symptoms and signs. In this broader sense, it sometimes includes injuries, disabilities, disorders, syndromes, infections, isolated symptoms, deviant behaviors, and atypical variations of structure and function, while in other contexts and for other purposes these may be considered distinguishable categories.

A symptom (from Greek σύμπτωμα, "accident, misfortune, that which befalls", from συμπίπτω, "I befall", from συν- "together, with" and πίπτω, "I fall") is a departure from normal function or feeling which is apparent to a patient, reflecting the presence of an unusual state, or of a disease.

In humans, disease is often used more broadly to refer to any condition that causes pain, dysfunction, distress, social problems, or death to the person afflicted, or similar problems for those in contact with the person.

Phenomena which commonly bring about death include aging, predation, malnutrition, disease, suicide, homicide, starvation, dehydration, and accidents or major trauma resulting in terminal injury.

In this broader sense, it sometimes includes injuries, disabilities, disorders, syndromes, infections, isolated symptoms, deviant behaviors, and atypical variations of structure and function, while in other contexts and for other purposes these may be considered distinguishable categories.

A syndrome is a set of medical signs and symptoms and collection of diseases which are not correlated with each other and often associated with a particular disease or disorder.

The study of disease is called pathology, which includes the study of etiology, or cause.

Pathology is the study of the causes and effects of disease or injury.

In humans, disease is often used more broadly to refer to any condition that causes pain, dysfunction, distress, social problems, or death to the person afflicted, or similar problems for those in contact with the person.

This is usually the result of acquired damage to the nerves, such as spinal cord injury, diabetes mellitus (diabetic neuropathy), or leprosy in countries where that disease is prevalent.

A disease may be caused by external factors such as pathogens or by internal dysfunctions.

In biology, a pathogen (πάθος pathos "suffering", "passion" and -γενής -genēs "producer of") in the oldest and broadest sense, is anything that can produce disease.

Diseases can also be classified in other ways, such as communicable versus non-communicable diseases.

A non-communicable disease (NCD) is a disease that is not transmissible directly from one person to another.

The study of disease is called pathology, which includes the study of etiology, or cause.

In medicine, the term refers to the causes of diseases or pathologies.

Terminal illness or end-stage disease is a disease that cannot be cured or adequately treated and is reasonably expected to result in death of the patient.

A complication in medicine, or medical complication, is an unfavorable result of a disease, health condition, or treatment.

Cures are a subset of treatments that reverse diseases completely or end medical problems permanently.

The medical condition could be a disease, mental illness, disability, or simply a condition a person considers socially undesirable, such as baldness or lack of breast tissue.

A sequela (, ; usually used in the plural, sequelae) is a pathological condition resulting from a disease, injury, therapy, or other trauma.

Evolutionary medicine or Darwinian medicine is the application of modern evolutionary theory to understanding health and disease.

Medicalization or medicalisation ([[American and British English spelling differences#-ise, -ize (-isation, -ization)|see spelling differences]]) is the process by which human conditions and problems come to be defined and treated as medical conditions, and thus become the subject of medical study, diagnosis, prevention, or treatment.

A passenger virus is a virus that is frequently found in samples from diseased tissue, such as tumours, but does not contribute to causing the disease.

Sickness behavior is a coordinated set of adaptive behavioral changes that develop in ill individuals during the course of an infection.

Occasionally those with other health problems may develop pneumonia.

A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma.

A functional disorder is a medical condition that impairs normal functioning of bodily processes that remains largely undetected under examination, dissection or even under a microscope.

A subclinically infected person is thus an asymptomatic carrier of a microbe, intestinal parasite, or virus that usually is a pathogen causing illness, at least in some individuals.

However, in certain conditions, some species are thought to be capable of causing disease by causing infection or increasing cancer risk for the host.

Pathophysiology ( physiopathology) – a convergence of pathology with physiology – is the study of the disordered physiological processes that cause, result from, or are otherwise associated with a disease or injury.

Medical state, also referred to as medical condition, is a term used to describe a hospital patient's health status.

It is distinct from "morbidity", which is either the prevalence or incidence of a disease, and also from the incidence rate (the number of newly appearing cases of the disease per unit of time).