What Is a Chronic Illness?

Take our Depression Test

Find a therapist to help with chronic illness

Many experiencing persistent physical symptoms are told by their doctors that there is no medical explanation.

The problem may be more to do with mainstream medicine's limited assumptions around what causes symptoms.

Medicine reduces symptoms to structural damage, delegitimizing symptoms that aren't explained by lab tests.

Mind-body dualism leaves little room for patients to do more than passively cope with "incurable" symptoms.

Most of my patients first come to see me in states of extreme confusion, frustration, and exasperation. They have commonly already seen a number of different doctors—generalists and specialists alike—in search of a coherent explanation for their symptoms, only to be routinely told that all tests have come back normal, and that no medical explanation for their suffering can be found.

Sometimes these patients are told that there’s nothing wrong with them. Sometimes, their doctors suggest that they may be suffering from an underlying disease that has not yet been uncovered by medical science. And sometimes, their doctor tells them that the problem is somehow all in their head.

At best, sufferers are offered diagnoses that turn out to offer a mere description of their symptoms, rather than an explanation or a pathway to treatment: think chronic pain syndrome, post-COVID-19 syndrome, chronic fatigue syndrome, and irritable bowel syndrome.

Research suggests that around a quarter of general practice patients experience significant persistent physical symptoms, and that roughly 10 percent have a history of multiple, distressing chronic symptoms.

Fortunately, a growing body of research from neuroscience and psychoneuroimmunology is offering scientifically robust explanations for why some people develop persistent physical symptoms, even in the apparent absence of an underlying disease.

What remains highly problematic is that most health professionals are not aware of this new science, nor of the emerging treatments that can help people to recover.

As a result, besides a possible referral to a counselor or psychologist to help the person learn to cope with their apparently inexplicable and incurable symptoms, many clinicians have come to believe that their job is complete once disease has been excluded as an explanation for their patients’ suffering.

This isn’t to vilify doctors who haven’t been trained in the latest science, but rather to draw attention to the sluggish failure of mainstream medicine to expand and update its core assumptions around health and illness.

So, what are these increasingly outdated assumptions that prevent medicine from being able to explain and treat persistent symptoms?

Unhelpful assumption 1: Analyzing biological phenomena at a microscopic level is the only way to understand and cure illness

Medicine is reductionistic. That’s not me being mean about it. Reductionism is the very word that medicine uses to describe its core project of analyzing human biology at a microscopic level in search of a single pathophysiological cause of illness.

Reductionism is based on Louis Pasteur’s “germ theory,” which emphasized the central role of the “germ”—namely, pathogens like bacterial and viral infections—in causing disease. This approach has been nothing short of miraculous in reducing human suffering at the hands of communicable disease, and it remains essential today.

What Is a Chronic Illness?

Take our Depression Test

Find a therapist to help with chronic illness

However, in the 21st century, much human suffering, especially in the Western world, is caused by chronic health conditions that do not have a single underlying cause. Instead, chronic illness typically has multiple interacting causes, including chronic stressors, exposure to toxins, and lifestyle factors, like diet, smoking, alcohol, and poor sleep.

Unhelpful assumption 2: All physical symptoms must have a single biological cause

Mainstream medicine also tends to presume that physical symptoms must always be reduced to a single biological cause. In other words, some kind of damage is done to the tissue of the body, and this directly results in symptoms, like pain, fatigue, nausea, or brain fog.

This model is logical and intuitive. But as my patients, and millions of others around the world know, sometimes it falls down. Commonly, there are symptoms, but tests indicate that the body is healthy.

Unhelpful assumption 3: Physical problems with a structural biological cause are more real and legitimate than physical problems without one

Very much standing on the shoulders of the first two assumptions, there is a strange implicit hierarchy in modern medicine. This hierarchy states that the suffering of people whose symptoms can be explained by lab tests is somehow more valid than that of individuals whose symptoms cannot be.

One day, hopefully, society will look back in shame at a health care system that practiced according to this arbitrary notion of what constitutes legitimate suffering.

Unhelpful assumption 4: The mind and body are completely separate entities

For several hundred years, Western thinking has separated mind and body. This view was most famously espoused by the 17th-century French philosopher René Descartes, whose theory of mind-body dualism argued that the mind and body are completely separate and could exist independently of each other.

While most medics today would not be quite as hard-line as this, it is striking to consider how we still live very much in line with this philosophy. We have separate hospitals and branches of medicine devoted to physical and mental health.

In the words of some pioneering researchers on persistent physical symptoms:

The divide of Western medical systems into either ‘physical’ or ‘mental’ health disciplines is arguably responsible for most controversies regarding MUS [medically unexplained symptoms], with physical and mental health specialists favoring distinct terms, diagnostic criteria and illness narratives for an overlapping set of complaints.

The divide of Western medical systems into either ‘physical’ or ‘mental’ health disciplines is arguably responsible for most controversies regarding MUS [medically unexplained symptoms], with physical and mental health specialists favoring distinct terms, diagnostic criteria and illness narratives for an overlapping set of complaints.

Unhelpful assumption 5: You can only hope to cope with persistent physical conditions

On the back of the failure of mainstream medicine to make sense of persistent physical symptoms, there has emerged a culture of overwhelming pessimism surrounding the expected health outcomes of people living with chronic fatigue, pain, and countless other symptoms.

Researchers at the University of Oxford interviewed teams of healthcare practitioners working with people living with conditions like fibromyalgia and ME/CFS. The research suggested that medics, charities, and government departments granting disability benefits all talk about these conditions—and require sufferers to talk about their own symptoms—in ways which reinforce the narrative that these are illnesses that the vast majority of people do not recover from.

The name of the research paper says it all: “Chronicity rhetoric in health and welfare systems inhibits patient recovery.”

Unhelpful assumption 6: Recovery from illness is a passive process

Finally, a medical model founded on acute, communicable illnesses teaches us that simply being prescribed the right antibiotic or antiviral medication is sufficient to get us back to health.

But for people living with persistent physical symptoms, which tend to have multiple interacting causal and sustaining factors, recovery from illness often requires a multi-pronged approach. The patient cannot afford to be a passive recipient of medical treatment; instead, they must take active ownership of their recovery.

If this prospect feels a little overwhelming, you may draw some inspiration from Sarahjane Belton, an associate professor of physical education, who wrote of her recovery from long COVID:

…confidence, and trust in myself, became central to my recovery. I started exercising autonomy and advocating for myself. I sought out specific help from health professionals when I knew what I needed. I trusted myself and my own growing body of knowledge and took full ownership of my recovery. I still met shaming experiences with health professionals but was able to quickly recover trust and confidence in myself.

…confidence, and trust in myself, became central to my recovery. I started exercising autonomy and advocating for myself. I sought out specific help from health professionals when I knew what I needed. I trusted myself and my own growing body of knowledge and took full ownership of my recovery. I still met shaming experiences with health professionals but was able to quickly recover trust and confidence in myself.

Abrahamsen, C., Beadsworth, M., Bostock, W., Chalder, T., Flottorp, S., Fors, E. A., ... & Vangelova-Korpinen, V. (2026). Persistent physical symptoms not explained by structural abnormalities or disease processes: a primary care approach to promote recovery. Scandinavian Journal of Primary Health Care, 44(1), 2633765.

Bell, V., Wilkinson, S., Greco, M., Hendrie, C., Mills, B., & Deeley, Q. (2020). What is the functional/organic distinction actually doing in psychiatry and neurology?. Wellcome Open Research, 5, 138.

Belton, S., & Sheridan, K. (2025). ‘The Second Arrow’: A Collaborative Autoethnographic Exploration of What Can Be Learned From One Long COVID Journey. Health Expectations, 28(3), e70227.

Cupit, C., Finlay, T., Pope, C., Hollick, R., Jones, G. T., Locock, L., ... & Basu, N. (2025). Chronicity rhetoric in health and welfare systems inhibits patient recovery: a qualitative, ethnographic study of fibromyalgia care. Social Science & Medicine, 382, 118313.

Fink, P., Toft, T., Hansen, M. S., Ørnbøl, E., & Olesen, F. (2007). Symptoms and syndromes of bodily distress: an exploratory study of 978 internal medical, neurological, and primary care patients. Biopsychosocial Science and Medicine, 69(1), 30-39.

Kiverstein, J., Kirchhoff, M. D., & Thacker, M. (2022). An embodied predictive processing theory of pain experience. Review of Philosophy and Psychology, 13(4), 973-998.

Körber, S., Frieser, D., Steinbrecher, N., & Hiller, W. (2011). Classification characteristics of the Patient Health Questionnaire-15 for screening somatoform disorders in a primary care setting. Journal of psychosomatic research, 71(3), 142-147.

Kroenke, K., Spitzer, R. L., DeGruy, F. V., Hahn, S. R., Linzer, M., Williams, J. B., ... & Davies, M. (1997). Multisomatoform disorder: an alternative to undifferentiated somatoform disorder for the somatizing patient in primary care. Archives of General Psychiatry, 54(4), 352-358.

Lekander, M. (2022). The Inflamed Feeling: The Brain's role in Immune Defence. Oxford University Press.

Löwe, B., Zipfel, S., van den Bergh, O., & Henningsen, P. (2025). Reconsidering persistent somatic symptoms: a transdiagnostic and transsymptomatic approach. Psychotherapy and psychosomatics, 94(1), 20-25.

Maté, G. (2024). The Myth of Normal: Trauma, Illness, and Healing in a Toxic Culture.

Rediger, J., & Rediger, J. (2020). Cured. Macmillan .

Van den Bergh, O., Witthöft, M., Petersen, S., & Brown, R. J. (2017). Symptoms and the body: taking the inferential leap. Neuroscience & Biobehavioral Reviews, 74, 185-203.

There was a problem adding your email address. Please try again.

By submitting your information you agree to the Psychology Today Terms & Conditions and Privacy Policy

© Psychology Today