"Multiple Chemical Sensitivity (MCS): A Spurious Diagnosis"

Stephen Barrett, M.D. at Quackwatch on Multiple Chemical Sensitivity ("MCS"):

…
Psychologist Herman Staudenmayer, Ph.D., of Denver, Colorado, has treated "MCS" patients for more than 30 years. He believes that although some people are very sensitive to various microorganisms, noxious chemicals, and common foods, there is no scientific evidence that an immunologic basis exists for generalized allergy to environmental substances. During the 1990s, like Rea, Staudenmayer and his colleague—the late John C. Selner, M.D. (an allergist)—used an environmental chamber to test sensitivity to airborne chemicals. However, they rejected clinical ecology theories and practices. Using well-designed double-blind tests, they demonstrated that "universal reactors" may develop multiple symptoms in response to the testing process without being allergic to any of the individual substances administered. One of their reports describes how they used an environmental chamber to evaluate 20 patients with multiple symptoms attributed to chemical hypersensitivity. These patients believed that they were reactive or hypersensitive to low-level exposure to many chemicals. Some had previously been evaluated and managed by clinical ecologists and diagnosed with "MCS." During nonblinded tests, these patients consistently reported symptoms they had associated with exposure at work, at home, or elsewhere. The environmental chamber enabled the patients to encounter measured amounts of purified air, compressed gasses, and air containing specific chemical concentrations, without knowing which situation was which. None of the patients demonstrated a response pattern implicating the chemicals supposedly responsible for their symptoms. Eighteen reported no symptoms at least once when the suspect chemical was present. Fifteen reported symptoms at least once when the suspect chemical was absent [10]. In other words, patients reacted to their feelings and beliefs about the test, rather than to the substance in question [11].

In 1999, the American Health Foundation's Environmental Health and Safety Council reached a similar conclusion. After reviewing the evidence for various alleged mechanisms though which odor-bearing chemicals might cause MCS symptoms, the council concluded:

In no case was there persuasive evidence that any olfactory mechanism involving fragrance underlies either induction of a sensitized state or the triggering of MCS symptoms. Fragrances and other odorants could, however, be associated with symptoms as claimed by MCS symptomatics, because they are recognizable stimuli, but fragrance has not been demonstrated to be causal in the usual sense. [12]

A more recent study tested whether "MCS" patients could reliably distinguish between airborne solvents and placebo and whether there were significant differences in measurable biological and neuropsychological parameters between solvent and placebo exposures. During the study, 20 MCS patients and 17 controls underwent six sessions in a challenge chamber in which they were exposed to solvent fumes and clean air in random order. Neither the patients nor the experimentors knew which exposures were which at the time they took place. No differences accuracy in identifying chemical exposure were found between the two groups. Nor was cognitive performance influenced by solvent exposure or different between the groups. Nor was there any difference between the groups in serum cortisol levels measured before and after exposures [13].

So probably no MCS, but other illnesses.

So what about the symptoms? They are interesting:

… The complaints associated with these labels include depression, irritability, mood swings, inability to concentrate or think clearly, poor memory, fatigue, drowsiness, diarrhea, constipation, dizziness, mental exhaustion (also called "brain fog" or "brain fag"), lightheadedness, sneezing, runny or stuffy nose, wheezing, itching eyes and nose, skin rashes, headache, chest pain, muscle and joint pain, urinary frequency, pounding heart, muscle incoordination, swelling of various parts of the body, upset stomach, tingling of the fingers and toes, and psychotic experiences associated with schizophrenia.

Well, some of it sounds like from ME/CFS, Fibromyalgia and POTS…

William J. Rea, M.D., who says he has treated more than 20,000 environmentally ill patients, states that they "may manifest any symptom in the textbook of medicine."

Oh my. If someone can diagnose literally anyone with MCS for having "any symptom in the textbook of medicine", then MCS is a worthless diagnose. And most certainly one will miss many other diagnoses, of real illnesses and diseases.