The academic forebear of the modern field of behavioral medicine and a part of the practice of consultation-liaison psychiatry, psychosomatic medicine integrates interdisciplinary evaluation and management involving diverse specialties including psychiatry, psychology, neurology, surgery, allergy, dermatology and psychoneuroimmunology. Clinical situations where mental processes act as a major factor affecting medical outcomes are areas where psychosomatic medicine has competence.
History of psychosomatics 
In the medieval Islamic world the Persian Muslim psychologist-physicians Ahmed ibn Sahl al-Balkhi (d. 934) and Haly Abbas (d. 994) developed an early understanding of illness that was due to the interaction of the mind and the body. They realized how a patient's physiology and psychology can have an effect on one another. They found correlations between patients who were physically and mentally healthy and between those who were physically and mentally ill.
Franz Alexander led in the beginnings of the 20th century, the movement looking for the dynamic interrelation between mind and body. Sigmund Freud pursued a deep interest in psychosomatic illnesses following his correspondence with Georg Groddeck who was, at the time, researching the possibility of treating physical disorders through psychological processes.
Since the 1970s, due to the work of Thure von Uexküll and his colleagues in Germany and elsewhere, biosemiotic theory has been used as a theoretical basis for psychosomatic medicine. Particularly, the umwelt concept and the theory of organism by Jakob von Uexküll has been found useful as an approach to describe psychosomatic phenomena.
Psychosomatic disorders 
Some physical diseases are believed to have a mental component derived from the stresses and strains of everyday living. This is the case, for example, of lower back pain and high blood pressure, which appear to be partly related to stresses in everyday life. Psychiatry has found it difficult until relatively recently to distinguish somatoform disorders, disorders in which mental factors are the sole cause of a physical illness, from psychosomatic disorders, disorders in which mental factors play a significant role in the development, expression, or resolution of a physical illness.
For instance, while peptic ulcer was once thought of as being purely caused by stress, later research revealed that Helicobacter pylori caused 80% of ulcers. However 4 out of 5 people colonised with Helicobacter pylori do not develop ulcers, and an expert panel convened by the Academy of Behavioral Medicine Research concluded that ulcers are not merely an infectious disease and that mental factors do play a significant role. One likelihood is that stress diverts energy away from the immune system, thereby stress promotes Helicobacter pylori infection in the body.
It is still difficult to classify some disorders as purely physical, mixed psychosomatic, or purely somatoform. One example is Irritable Bowel Syndrome (IBS) that was considered formerly as having purely mental causes, while subsequent research showed significant differences in the behaviour of the gut in IBS patients. On the other hand, there are no actual structural changes in IBS patients and research shows that stress and emotions are still significant factors in causing IBS.
However, while it is necessary to identify if an illness has a physical basis, it is recognized more and more that the effort to identify disorders as purely physical or mixed psychosomatic is increasingly obsolete as almost all physical illness have mental factors that determine their onset, presentation, maintenance, susceptibility to treatment, and resolution.
Addressing such factors is the remit of the applied field of behavioral medicine. In modern society, psychosomatic aspects of illness are often attributed to stress making the remediation of stress one important factor in the development, treatment, and prevention of psychosomatic illness.
Connotations of the term "psychosomatic illness" 
Psychosomatic medicine is not to be confused with the demotic and scientifically incorrect use of the phrase "psychosomatic illness," particularly the influence the mind has over physical processes — including the manifestations of disabilities that are based on intellectual infirmities, rather than actual injuries or physical limitations. These are exemplified by phrases such as the power of suggestion, the use of "positive thinking" and concepts like "mind over matter" to apply to illnesses that are now called somatoform disorders. Such illness is classified as neurotic, stress-related and somatoform disorders by the World Health Organization in the International Statistical Classification of Diseases and Related Health Problems. The field of psychosomatic medicine fell into disrepute clinically due to this incorrect use of this term, which was largely due to the influence of psychoanalytic theory on psychiatric physicians and the inaccurate application by non-specialists in the first part of the 20th century who considered this form of illness to be akin to malingering, thereby further harming the sufferer. For this reason, among others, the field of Behavioral Medicine has taken over much of the remit of Psychosomatic Medicine in practice and there exist large areas of overlap in the scientific research.
See also 
- Behavioral Medicine
- Conversion disorder
- Healing Words: Poetry and Medicine (documentary film)
- Placebo Effect
- Psychosomatic Medicine (the journal)
- Somatoform disorder
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