How an Organic Disease Differs From a Functional Disorder

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Organic disease is one in which measurable changes are detected in cells, tissues, or organs of the body. In contrast, a functional disease causes symptoms, but the disease process is either unknown or it can't be measured by an agreed-upon scientific method or standard.

For example, abnormalities in a person's blood cell counts may point to an organic disease like cancer. In contrast, a functional disorder like fibromyalgia can be diagnosed despite there being no similar evidence to confirm it.

This article explains the difference between functional and organic diseases and lists some common examples of each. It also discusses difficulties in diagnosis, which is often the case with symptoms associated with mental health or psychosomatic disorders.

Doctor checking X-Ray with patient
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Examples of Organic Disease

Organic disease is a classification for many different types of illness. They can be localized (meaning they affect a specific part of the body) or systemic (affecting multiple organ systems).

They can be inherited (genetic) or caused by external or environmental forces. Some organic diseases are communicable, passed from one person to the next, while others are non-communicable.

Some of the broader categories and types of organic diseases include cancer, inflammatory illness, autoimmune diseases, and infectious disease.

Autoimmune Diseases

Autoimmune disease occurs when the body's immune system attacks its own cells and tissues. Examples include:


Cancer occurs when abnormal cells multiply unchecked and overtake healthy cells. Specific types of the cancers that are organic diseases include:

Inflammatory Diseases

Inflammatory diseases cause acute or progressive damage to cells and tissues due to inflammation. They include:

Infectious Diseases

Infectious diseases occur when a bacteria, virus, fungus, parasite, or other microbe is transmitted between individuals. These diseases include:

Bad Breath and Organic Disease

Halitosis, or bad breath, is an example of a health condition that's not always well understood. An organic disease process is at work in about 60% of cases, such as the lung condition bronchiectasis. But there's no underlying organic disease in 40% of people who experience it.

Examples of Functional Disorders

A non-organic disease is typically referred to as being functional, meaning that there are symptoms of illness but no clear measures by which to make a diagnosis.

The absence of measurable biomarkers doesn't mean that functional diseases don't exist; it simply means the causes are unknown (idiopathic).

Pruritus (itching) is one such example of a functional symptom. On its own, it is associated with neither a physical or biochemical change but remains a very real and tangible sensation. The same applies to:

  • Fatigue
  • Chronic headaches
  • Insomnia

Examples of functional disorders defined and classified by their symptoms include:

Epilepsy, migraine, and Alzheimer's disease were once considered functional disorders until scientific advances clarified they are actually organic.

Functional vs. Psychosomatic Symptoms

Psychiatric illnesses are also largely considered functional since the underlying cause is not readily identified. These include:

  • Clinical depression
  • Bipolar disorder
  • Schizophrenia
  • Attention deficit hyperactivity disorder (ADHD)
  • Obsessive-compulsive disorder (OCD)
  • Post-traumatic stress syndrome (PTSD)

However, a psychiatric illness is not the same thing as a psychosomatic one. Psychosomatic symptoms are those that are believed to be derived from the stresses and strains of everyday living.

They are driven by a person's mental or emotional state and often manifest with symptoms of:

Functional symptoms differ from psychosomatic ones in that the removal of the emotional stress may lessen the severity of symptoms but not entirely erase them.

In the past, functional disorders were largely considered psychosomatic. These conditions are now understood as having distinctive characteristics that define them irrespective of a person's emotional state.


Health conditions and disorders are typically described as being either an organic disease or a functional disease. The difference lies in the ability to measure and validate a diagnosis based on biomarkers for the disease and agreed-upon standards of identifying them.

Organic disease can be clearly identified, while functional disease remains idiopathic, or without a clear cause. It's not that functional diseases don't exist, but rather the shared understanding of the evidence for them.

Over time, medical advances have changed how certain functional diseases are now understood. It's likely that researchers will identify pathways to better identify organic disease processes at the root of illnesses now categorized as functional.

2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Scully C. Halitosis. BMJ Clin Evid. 2014 Sep 18;2014:1305. PMID: 25234037

  2. Maffei ME. Fibromyalgia: Recent Advances in Diagnosis, Classification, Pharmacotherapy and Alternative Remedies. Int J Mol Sci. 2020 Oct 23;21(21):7877. doi:10.3390/ijms21217877.

By Barbara Bolen, PhD
Barbara Bolen, PhD, is a licensed clinical psychologist and health coach. She has written multiple books focused on living with irritable bowel syndrome.