The 20th-century science of psychology emerged from the 19th-century attitude to mental health as an illness requiring medical intervention, the province of psychiatry instead of psychology. This model was increasingly questioned, however, with some psychologists questioning the existence of mental health altogether. Obviously, there are biological causes of some psychological problems.
This could be actual mental impairment through injury, degeneration, or disease, including such things as strokes or Alzheimer’s disease, or, less obviously, physical diseases affecting the nervous system that might be genetic in origin. However, there are also cases where symptoms are caused by purely psychological factors; these might include anxiety disorders, phobias, or compulsions. Some people, however, continue to argue that these conditions should not be classified as psychiatric illnesses because they do not meet the criteria for being a medical illness.
