Sharon calls herself a universal reactor. In the 1990s, she became allergic to the world, to the mould colonising her home and the paint coating her kitchen walls, but also deodorants, soaps and anything containing plastic. Public spaces rife with artificial fragrances were unbearable. Scented disinfectants and air fresheners in hospitals made visiting doctors torture. The pervasiveness of perfumes and colognes barred her from in-person social gatherings. Even stepping into her own back garden was complicated by the whiff of pesticides and her neighbours laundry detergent sailing through the air. When modern medicine failed to identify the cause of Sharons illness, exiting society felt like her only solution. She started asking her husband to strip and shower every time he came home. Grandchildren greeted her through a window. When we met for the first time, Sharon had been housebound for more than six years.

When I started medical school, the formaldehyde-based solutions used to embalm the cadavers in the human anatomy labs would cause my nose to burn and my eyes to well up representing the mild, mundane end of a chemical sensitivity spectrum. The other extreme of the spectrum is an environmental intolerance of unknown cause (referred to as idiopathic by doctors) or, as it is commonly known, multiple chemical sensitivity (MCS). An official definition of MCS does not exist because the condition is not recognised as a distinct medical entity by the World Health Organization or the American Medical Association, although it has been recognised as a disability in countries such as Germany and Canada.

Disagreement over the validity of the disease is partially due to the lack of a distinct set of signs and symptoms, or an accepted cause. When Sharon reacts, she experiences symptoms from seemingly every organ system, from brain fog to chest pain, diarrhoea, muscle aches, depression and odd rashes. There are many different triggers for MCS, sometimes extending beyond chemicals to food and even electromagnetic fields. Consistent physical findings and reproducible lab results have not been found and, as a result, people such as Sharon not only endure severe, chronic illness but also scrutiny over whether their condition is real.

The first reported case of MCS was published in the Journal of Laboratory and Clinical Medicine in 1952 by the American allergist Theron Randolph. Although he claimed to have previously encountered 40 cases, Randolph chose to focus on the story of one woman, 41-year-old Nora Barnes. She had arrived at Randolphs office at Northwestern University in Illinois with a diverse and bizarre array of symptoms. A former cosmetics salesperson, she represented an extreme case. She was always tired, her arms and legs were swollen, and headaches and intermittent blackouts ruined her ability to work. A doctor had previously diagnosed her with hypochondria, but Barnes was desperate for a real diagnosis.

Randolph noted that the drive into Chicago from Michigan had worsened her symptoms, which spontaneously resolved when she checked into her room on the 23rd floor of a hotel where, Randolph reasoned, she was far away from the noxious motor exhaust filling the streets. In fact, in his report Randolph listed 30 substances that Barnes reacted to when touched (nylon, nail polish), ingested (aspirin, food dye), inhaled (perfume, the burning of pine in fireplace) and injected (the synthetic opiate meperidine, and Benadryl).

He posited that Barnes and his 40 other patients were sensitive to petroleum products in ways that defied the classic clinical picture of allergies. That is, rather than an adverse immune response, such as hives or a rash where the body is reacting to a particular antigen, patients with chemical sensitivities were displaying an intolerance. Randolph theorised that, just as people who are lactose-intolerant experience abdominal pain, diarrhoea and gas because of undigested lactose creating excess fluid in their gastrointestinal tract, his patients were vulnerable to toxicity at relatively low concentrations of certain chemicals that they were unable to metabolise. He even suggested that chemical sensitivity research was being suppressed by the ubiquitous distribution of petroleum and wood products. MCS, he believed, was not only a matter of scientific exploration, but also of deep-seated corporate interest. Randolph concludes his report with his recommended treatment: avoidance of exposure.

In that one-page abstract, Randolph cut the ribbon on the completely novel but quickly controversial field of environmental medicine. Nowadays, we hardly question the ties between the environment and wellbeing. The danger of secondhand smoke, the realities of climate change and the endemic nature of respiratory maladies such as asthma are common knowledge. The issue was that Randolphs patients lacked abnormal test results (specifically, diagnostic levels of immunoglobulin E, a blood marker that is elevated during an immune response). Whatever afflicted them were not conventional allergies, so conventional allergists resisted Randolphs hypotheses.

Randolph was in the dark. Why was MCS only now rearing its head? He also asked another, more radical question: why did this seem to be a distinctly American phenomenon? After all, the only other mention of chemical sensitivities in medical literature was in the US neurologist George Miller Beards 1880 textbook A Practical Treatise on Nervous Exhaustion (Neurasthenia). Beard argued that sensitivity to foods containing alcohol or caffeine was associated with neurasthenia, a now-defunct term used to describe the exhaustion of the nervous system propagated by the USs frenetic culture of productivity. Like Beard, Randolph saw chemical sensitivities as a disease of modernity, and conceived the origin as wear-and-tear as opposed to overload.

Randolph proposed that Americans, propelled by the post-second world war boom, had encountered synthetic chemicals more and more in their workplaces and homes, at concentrations considered acceptable for most people. Chronic exposure to these subtoxic dosages, in conjunction with genetic predispositions, strained the body and made patients vulnerable. On the back of this theory, Randolph developed a new branch of medicine and, with colleagues, founded the Society for Clinical Ecology, now known as the American Academy of Environmental Medicine.

As his professional reputation teetered, his popularity soared and patients flocked to his care. Despite this growth in interest, researchers never identified blood markers in MCS patients, and trials found that people with MCS couldnt differentiate between triggers and placebos. By 2001, a review in the Journal of Internal Medicine found MCS virtually nonexistent outside western industrialised countries, despite the globalisation of chemical use, suggesting that the phenomenon was culturally bound.

MCS subsequently became a diagnosis of exclusion, a leftover label used after every other possibility was eliminated. The empirical uncertainty came to a head in 2021, when Quebecs public health agency, the INSPQ, published an 840-page report that reviewed more than 4,000 articles in the scientific literature, concluding that MCS is an anxiety disorder. In medicine, psychiatric disorders are not intrinsically inferior; serious mental illness is, after all, the product of neurological dysfunction. But the MCS patients I spoke to found the language offensive and irresponsible. Reducing what they felt in their eyes, throats, lungs and guts to anxiety was not acceptable at all.

As a woman I will call Judy told me: I would tell doctors my symptoms, and then theyd run a complete blood count and tell me I looked fine, that it must be stress, so theyd shove a prescription for an antidepressant in my face and tell me to come back in a year. In fact, because MCS is so stigmatising, such patients may never receive the level of specialised care they need. In the wake of her treatment, Judy was frequently bedbound from crushing fatigue, and no one took her MCS seriously. I think a lot of doctors fail to understand that we are intelligent, she said. A lot of us with chemical sensitivities spend a good amount of our time researching and reading scientific articles and papers. I probably spent more of my free time reading papers than most doctors.

Judy grew up in Texas, where she developed irritable bowel syndrome and was told by doctors that she was stressed. Her 20s were spent in Washington state where she worked as a consultant before a major health crash left her bedbound for years (again, the doctors said she was stressed). Later, after moving to Massachusetts, a new paint job at her home gave her fatigue and diarrhoea. She used to browse the local art museum every Saturday, but even fumes from the paintings irritated her symptoms. She visited every primary care doctor in her city, as well as gastroenterologists, cardiologists, neurologists, endocrinologists and even geneticists. Most of them reacted the same way: with a furrowed brow and an antidepressant prescription in hand. Not one allopathic doctor has ever been able to help me, Judy said.

Morton Teich is one of the few physicians who diagnoses and treats patients with MCS in New York. The entrance to his integrative medicine private practice is hidden away behind a side door in a grey-brick building on Park Avenue. As I entered the waiting room, the first thing to catch my eye was the monstrous mountain of folders and binders precariously hugging a wall, in lieu of an electronic medical record. I half-expected Teichs clinic to resemble the environmental isolation unit used by Randolph in the 1950s, with an airlocked entrance, blocked ventilation shafts and stainless-steel air-filtration devices, books and newspapers in sealed boxes, aluminium walls to prevent electromagnetic pollution, and water in glass bottles instead of a cooler. But there were none of the above. The clinic was like any other family medicine practice I had seen before; it was just very old. The physical examination rooms had brown linoleum floors and green metal chairs and tables. And there were no windows.

Although several of Teichs patients were chemically sensitive, MCS was rarely the central focus of visits. When he introduced me, as a student writing about MCS, to his first patient of the day, a petrol-intolerant woman whose appointment was over the phone because she was housebound, she admitted to never having heard of the condition. You have to remember, Teich told me, that MCS is a symptom. Its just one aspect of my patients problems. My goal is to get a good history and find the underlying cause. Later, when I asked him whether he had observed any patterns suggesting an organic cause of MCS, he responded: Mould. Almost always.

Many people with MCS I encountered online also cited mould as a probable cause. Sharon told me about her first episode in 1998, when she experienced chest pain after discovering black mould festering in her familys trailer home. A cardiac examination had produced no remarkable results, and Sharons primary care physician declared that she was having a panic attack related to the stress of a recent miscarriage. Sharon recognised that this contributed to her sudden health decline, but also found that her symptoms resolved only once she began sleeping away from home.

She found recognition in medical books such as Toxic (2016) by Neil Nathan, a retired family physician who argued that bodily sensitivities were the product of a hyper-reactive nervous system and a vigilant immune system that fired up in reaction to toxicities, much as Randolph had said. The conditions that Nathan describes are not supported by academic medicine as causes of MCS: mould toxicity and chronic Lyme disease are subject to the same critique.

Sharon went to see William Rea, a former surgeon (and Teichs best friend). Rea diagnosed her with MCS secondary to mould toxicity. Mould is everywhere, Teich told me. Not just indoors. Mould grows on leaves. Thats why people without seasonal allergies can become chemically sensitive during autumn. When trees shed their leaves, he told me, mould spores fly into the air. He suspected that American mould is not American at all, but an invasive species that rode wind currents over the Pacific from China. He mentioned in passing that his wife recently died from ovarian cancer. Her disease, he speculated, also had its roots in mould.

In fact, Teich commonly treats patients with nystatin, an antifungal medication used to treat candida yeast infections, which often infect the mouth, skin and vagina. I have an 80% success rate, he told me. I was dubious that such a cheap and commonplace drug was able to cure an illness as debilitating as MCS, but I could not sneer at his track record. Every patient I met while shadowing Teich was comfortably in recovery, with smiles and jokes, miles apart from the people I met in online support groups who seemed to be permanently in the throes of their illness.

However, Teich was not practising medicine as I was taught it. This was a man who believed that the recombinant MMR vaccine could trigger acute autism traditionally an anti-science point of view. When one of his patients, a charismatic bookworm Ill call Mark, arrived at an appointment with severe, purple swelling up to his knees and a clear case of stasis dermatitis (irritation of the skin caused by varicose veins), Teich reflexively blamed mould and wrote a prescription for nystatin instead of urging Mark to see a cardiologist. When I asked how a fungal infection in Marks toes could cause such a bad rash on his legs, he responded: We have candida everywhere, and its toxins are released into the blood and travel to every part of the body. The thing is, most people dont notice until its too late.

Moulds and fungi are easy scapegoats for inexplicable illnesses because they are so ubiquitous in our indoor and outdoor environments. A great deal of concern over mould toxicity (or, to use the technical term, mycotoxicosis) stems from the concept of sick-building syndrome, in which visible black mould is thought to increase sensitivity and make people ill. This was true of Mark, who could point to the demolition of an old building across the street from his apartment as a source of mould in the atmosphere. Yet in mainstream medicine, diseases caused by moulds are restricted to allergies, hypersensitivity pneumonitis (an immunologic reaction to an inhaled agent, usually organic, within the lungs) and infection. Disseminated fungal infections occur almost exclusively in patients who are immunocompromised, hospitalised or have an invasive foreign body such as a catheter. Furthermore, if clinical ecologists such as Teich are correct that moulds such as candida can damage multiple organs, then it must be spreading through the bloodstream. But I have yet to encounter a patient with MCS who reported fever or other symptoms of sepsis (the traumatic, whole-body reaction to infection) as part of their experience.

Teich himself did not use blood cultures to verify his claims of systemic candidiasis, and instead looked to chronic fungal infection of the nails, common in the general population, as sufficient proof.

I dont need tests or blood work, he told me. I rarely ever order them. I can see with my eyes that he has mould, and thats enough. It was Teichs common practice to ask his patients to remove their socks to reveal the inevitable ridges and splits on their big toenails, and thats all he needed.

Through Teich, I met a couple who were both chemically sensitive but otherwise just regular people. The wife, an upper-middle-class white woman I will call Cindy, had a long history of allergies and irritable bowel syndrome. She became ill whenever she smelled fumes or fragrances, especially laundry detergent and citrus or floral scents. Teich put both her and her husband on nystatin, and their sensitivities lessened dramatically.

What struck me as different about her case, compared with other patients with MCS, was that Cindy was also on a course of antidepressants and cognitive behavioural therapy, the standard treatment for anxiety and depression. It really helps to cope with all the stress that my illness causes. You learn to live despite everything, she said.

In contemporary academic medicine, stress and anxiety cause MCS, but MCS can itself cause psychiatric symptoms. Teich later told me, unexpectedly, that he had no illusions about whether MCS is a partly psychiatric illness: Stress affects the adrenals, and that makes MCS worse. The mind and the body are not separate. We have to treat the whole person.

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To understand this case, I also spoke to Donald Black, associate chief of staff for mental health at the Iowa City Veterans Administration Health Care. He co-authored a recent article on idiopathic environmental intolerance that took a uniform stance on MCS as a psychosomatic disorder. In 1988, when Black was a new faculty member at the University of Iowa, he interviewed a patient entering a drug trial for obsessive-compulsive disorder. He asked the woman to list her medications, and watched as she started unloading strange supplements and a book about environmental illness from her bag.

The woman had been seeing a psychiatrist in Iowa City a colleague of Blacks who had diagnosed her with systemic candidiasis. Black was flummoxed. If that diagnosis was true, then the woman would be very ill, not sitting calmly before him. Besides, it was not up to a psychiatrist to treat a fungal infection. How did he make the diagnosis? Did he do a physical or run blood tests? No, the patient told him, the psychiatrist just said that her symptoms were compatible with candidiasis. These symptoms included chemical sensitivities. After advising the patient to discard her supplements and find a new psychiatrist, Black made some phone calls and discovered that, indeed, his colleague had fallen in with the clinical ecologists.

Black was intrigued by this amorphous condition that had garnered an endless number of names: environmentally induced illness, toxicant-induced loss of tolerance, chemical hypersensitivity disease, immune dysregulation syndrome, cerebral allergy, 20th-century disease, and mould toxicity. In 1990, he solicited the aid of a medical student to find 26 subjects who had been diagnosed by clinical ecologists with chemical sensitivities and to conduct an emotional profile. Every participant in their study filled out a battery of questions that determined whether they satisfied any of the criteria for psychiatric disorders. Compared with the controls, the chemically sensitive subjects had 6.3 times higher lifetime prevalence of major depression, and 6.8 times higher lifetime prevalence of panic disorder or agoraphobia; 17% of the cases met the criteria for somatisation disorder (an extreme focus on physical symptoms such as pain or fatigue that causes major emotional distress and problems functioning).

In my own review of the literature, it was clear that the most compelling evidence for MCS came from case studies of large-scale initiating events such as the Gulf war (where soldiers were uniquely exposed to pesticides and pyridostigmine bromide pills to protect against nerve agents) or the terrorist attacks on the US of 11 September 2001 (when toxins from the falling towers caused cancers and respiratory ailments for years). In both instances, a significant number of victims developed chemical intolerances compared with populations who were not exposed. From a national survey of veterans deployed in the Gulf war, researchers found that up to a third of respondents reported multi-symptom illnesses, including sensitivity to pesticides twice the rate of veterans who had not deployed. Given that Gulf war veterans experienced post-traumatic stress disorder at levels similar to those in other military conflicts, the findings have been used to breathe new life into Randolphs idea of postindustrial toxicities leading to intolerance. The same has been said of the first responders and the World Trade Centres nearby residents, who developed pulmonary symptoms when exposed to cigarette smoke, vehicle exhaust, cleaning solutions, perfume, or other airborne irritants after 9/11, according to a team at Mount Sinai.

Black, who doubts a real disease, has no current clinical experience with MCS patients. (Apart from the papers he wrote more than 20 years ago, he had seen only a handful of MCS patients over the course of his career.) Despite this, he had not only written the article about MCS, but also a guide in a major online medical manual on how to approach MCS treatment as a psychiatric disease. When I asked him if there was a way for physicians to regain the trust of patients who have been bruised by the medical system, he simply replied: No. For him, there would always be a subset of patients who are searching for answers or treatments that traditional medicine could not satisfy. Those were the people who saw clinical ecologists, or who left society altogether. In a time of limited resources, these were not the patients on which Black thought psychiatry needed to focus.

It became clear to me why even the de facto leading professional on MCS had hardly any experience actually treating MCS. In his 1990 paper, Black then a young doctor rightly observed that traditional medical practitioners are probably insensitive to patients with vague complaints, and need to develop new approaches to keep them within the medical fold. The study subjects clearly believed that their clinical ecologists had something to offer them that others did not: sympathy, recognition of pain and suffering, a physical explanation for their suffering, and active participation in medical care.

I wondered if Black had given up on these new approaches because few MCS patients wanted to see a psychiatrist in the first place.

Physicians on either side of the debate agreed that mental illness is a crucial part of treating MCS, with one I spoke to believing that stress causes MCS, and another believing that MCS causes stress. To reconcile the views, I interviewed another physician, Christine Oliver, a doctor of occupational medicine in Toronto, where she has served on the Ontario Task Force on Environmental Health. Oliver believes that both stances are probably valid and true. No matter what side youre on, she told me, theres a growing consensus that this is a public health problem.

Oliver represents a useful third position, one that takes the MCS illness experience seriously while sticking closely to medical science. As one of few MCS-agnostic physicians, she believes in a physiological cause for MCS that we cannot know and therefore cannot treat directly due to lack of research. Oliver agrees with Randolphs original suggestion of avoiding exposures, although she understands that this approach has resulted in traumatising changes in patients abilities to function. For her, the priority for MCS patients is a practical one: finding appropriate housing. Often unable to work and with a limited income, many of her patients occupy public housing or multi-family dwellings. The physician of an MCS patient must act like a social worker. Facilities such as hospitals, she feels, should be made more accessible by reducing scented cleaning products and soaps. Ultimately, finding a non-threatening space with digital access to healthcare providers and social support is the best way to allow the illness to run its course.

Whether organic or psychosomatic or something in between, MCS is a chronic illness. One of the hardest things about being chronically ill, wrote the American author Meghan ORourke in the New Yorker in 2013 about her battle against Lyme disease, is that most people find what youre going through incomprehensible if they believe you are going through it. In your loneliness, your preoccupation with an enduring new reality, you want to be understood in a way that you cant be.

A language for chronic illness does not exist beyond symptomatology, because in the end symptoms are what debilitate normal human functioning. In chronic pain, analgesics can at least deaden a patients suffering. The same cannot be said for MCS symptoms, which are disorienting in their chaotic variety, inescapability and inexpressibility. There are few established avenues for patients to completely avoid triggering their MCS, and so they learn to orient their lives around mitigating symptoms instead, whether that is a change in diet or moving house, as Sharon did. MCS comes to define their existence.

As a housebound person, Sharons ability to build a different life was limited. Outside, the world was moving forward, yet Sharon never felt left behind. What allowed her to live with chronic illness was not medicine or therapy, but the internet. On a typical day, Sharon wakes up and prays in bed. She wolfs down handfuls of pills and listens to upbeat music on YouTube while preparing her meals for the day: blended meats and vegetables, for easier swallowing. The rest of the day is spent on her laptop computer, checking email and Facebook, watching YouTube videos until her husband returns home in the evening. Then bed. This is how Sharon has lived for the past six years, and she does not expect anything different from the future. When I asked her if being homebound was lonely, I was taken aback at her reply: No.

In spite of not having met most of her 15 grandchildren (with two more on the way), Sharon keeps in daily contact with all of them. In fact, Sharon communicates with others on a nearly constant basis. Some people are very much extroverts, Sharon wrote. I certainly am. But there are also people who need physical touch and I can understand why they might need to see real people then but its very possible to be content with online friends. This is my life! The friendships that Sharon formed online with other housebound people with chronic illnesses were the longest-lasting and the most alive relationships she had ever known. She had never met her best friend of 20 years their relationship existed completely through letters and emails, until two years ago, when the friend died. That was very hard for me, Sharon wrote.

The pandemic changed very little of Sharons life. If anything, Covid-19 improved her situation. Sharons local church live-streamed Sunday service, telehealth doctor appointments became the default, YouTube exploded in content, and staying indoors was normalised. Sharon saw her network steadily expand as more older adults became isolated in quarantine.

People within the online MCS community call themselves canaries, after the birds historically used as sentinels in coalmines to detect toxic levels of carbon monoxide. With a higher metabolism and respiratory rate, the small birds would theoretically perish before the less-sensitive human miners, providing a signal to escape. The question for people with MCS is: will anyone listen?

Us canaries, said a woman named Vera, who was bedbound from MCS for 15 years after a botched orthopaedic surgery, we struggle and suffer in silence. Now, in the information age, they have colonised the internet to find people like themselves. For our part, we must reimagine chronic illness which will become drastically more common in the aftermath of the pandemic where what matters to the patient is not only a scientific explanation and a cure, but also a way to continue living a meaningful life. This calls into action the distinction between illness and disease that the psychiatrist and anthropologist Arthur Kleinman made in his 1988 book The Illness Narratives. Whereas a disease is an organic process within the body, illness is the lived experience of bodily processes. Illness problems, he writes, are the principal difficulties that symptoms and disability create in our lives.

By centring conversations about MCS on whether or not it is real, we alienate the people whose illnesses have deteriorated their ability to function at home and in the world. After all, the fundamental mistrust does not lie in the patient-physician relationship, but between patients and their bodies. Chronic illness is a corporeal betrayal, an all-out assault on the coherent self. Academic medicine cannot yet shed light on the physiological mechanisms that would explain MCS. But practitioners and the rest of society must still meet patients with empathy and acceptance, making space for their narratives, their lives, and their experience in the medical and wider world.

This essay was originally published in Aeon

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Allergic to the world: can medicine help people with severe intolerance to chemicals? - The Guardian