Prevalence of Multiple Chemical Sensitivity in Canada Between 2000 and 2020, 2026, Robins et al

forestglip

forestglip

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Prevalence of Multiple Chemical Sensitivity in Canada Between 2000 and 2020

Robins, Stephanie; Molot, John; Peris, Rohini

Abstract
Multiple chemical sensitivity (MCS) describes an acquired condition characterized by recurrent, non-specific symptoms attributed to previously tolerated chemical exposure. Although Canada collects national data on MCS through population health surveys, the condition remains poorly understood and under-studied.

This study analyzes data from the Canadian Community Health Survey (2000–2020) to examine trends in MCS prevalence across demographic characteristics, including province of residence, sex, and age. Descriptive analyses were used to assess temporal changes and differences between regions and population subgroups.

Between 2000 and 2020, the proportion of Canadians reporting an MCS diagnosis increased from 1.9% to 3.5%. Prevalence varied geographically, with higher rates consistently observed in the Atlantic provinces compared with the Prairie provinces. MCS prevalence increased with age in both sexes; however, rates were higher among young males than females, with this pattern reversing in mid-life as prevalence became higher among females.

These findings provide a national overview of MCS prevalence over two decades and offer relevant information for public health authorities, healthcare professionals, and researchers. The observed prevalence aligns with international estimates, underscoring MCS as an emerging public health concern in Canada.

Web | DOI | PDF | International Journal of Environmental Research and Public Health | Open Access
 
That's a really tricky topic, since AFAIK, there's no clinical test to prove MCS. Thus prevalence depends on how likely such claims are accepted, which might be a result of social media, economic environment, politics, etc. Imagine two scenarios: one in which a popular TV show paints MCS as a valid biological problem, vs one where the show paints it as nonsense to be made fun of. I expect the two would show dramatically different "prevalence" reported afterwards.

The same holds true for ME: without a clinical test, the prevalence has low precision.
 
Creekside said:
The same holds true for ME: without a clinical test, the prevalence has low precision.
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I think there is a big difference. The prevalence of ME/CFS is now widely agreed to fall within a range of the sort we see for conditions like rheumatoid arthritis. The uncertainty is somewhere between twofold and five fold and getting nearer the twofold. Because of a large proportion of reltively mild cases RA is as vague as that, despite there being tests.

But for multiple chemical sensitivity estimates of prevalence are likely to vary by 100 fold or even infinity because many physicians would not recognise it at all. The problem, as for MCAS, is that it is adiagnosis based on a causal attribution. For multiple chemical sensitivity that seems to be almost completely speculative:

forestglip said:
an acquired condition characterized by recurrent, non-specific symptoms attributed to previously tolerated chemical exposure
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Attributed by whom? On what basis?

I think the MCS concept is interesting in that it focuses on chemical intolerances and ME/CFS might have quite a bit to do with intolerances based on chemical signals - maybe even olfactomedin mediated. But as far as i know the concept of MCS is not linked to any proposed mediating mechanism and remains just a free-floating attribution of cause.
 
Jonathan Edwards said:
forestglip said:
an acquired condition characterized by recurrent, non-specific symptoms attributed to previously tolerated chemical exposure
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Attributed by whom? On what basis?
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I assume they mean attributed by the patient, in which case it doesn't sound that different from how ME/CFS could plausibly be described:
an acquired condition characterized by recurrent, non-specific symptoms attributed to previously tolerated exertion
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It’s a bit more complicated than what the abstract says:

A clinical diagnosis of MCS is based on six consensus-based criteria:
  1. the symptoms are reproducible with [repeated] chemical exposure;
  2. the condition is chronic;
  3. low levels of exposure [lower than previously or commonly tolerated] result in manifestation of the syndrome;
  4. the symptoms improve or resolve when the incitants are removed;
  5. responses occur to multiple chemically unrelated substances;
  6. symptoms involve multiple organ systems
 
forestglip said:
I assume they mean attributed by the patient, in which case it doesn't sound that different from how ME/CFS could plausibly be described:
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I don't think they do. My impression is that MCS is handed out as a diagnosis to people who very likely have ME/CFS on the basis that the physician concludes from leading questions that chemicals were the cause.

And ME/CFS does not work like that either. People with ME/CFS do not attribute their problems to exertion so much as to there being something badly wrong that results in normal exertion being followed by feeling ill. Many probably do not even relate their symptoms to exertion until it has been suggested to them. We have members here who had no idea of the idea of PEM until years on.
 
Maybe the wording of the criteria posted above could be improved to not imply causality, but it doesn't sound all that different from ME/CFS, just with random chemicals instead of exertion. And probably different timeline and effects. But the criteria doesn't seem to imply that any specific chemical metabolism is causing symptoms.

People with ME/CFS seem to be sensitive to things like perfumes. I think it's plausible many people are similar, but without the exertion part.

I'd like to know if this sensitivity exists even if a person can't smell the chemical.
 
Utsikt said:
It’s a bit more complicated than what the abstract says:

A clinical diagnosis of MCS is based on six consensus-based criteria:
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OK, but since we know that people are very unreliable about attributing cause and that many are suggestible to physicians proposed explanations, and chemical exposure is a pretty loaded word, I think it remains pretty shaky as diagnostic category.
 
forestglip said:
People with ME/CFS seem to be sensitive to things like perfumes. I think it's plausible many people are similar, but without the exertion part.
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Agreed. The other thing that seems too vague is the definition in terms of 'non-specifc symtpoms', which could be just about anything.

I think the biggest problem is that the vast majority of physicians will never make this diagnosis or see the need to and so diagnostic rates are likely simply to reflect gossip amongst medics in this or that town or country.
 
Jonathan Edwards said:
We have discussed it quite a bit on the OLFM4 Genetics thread I think. DecodeME found a potential link to OLFM4 which is an olfactomedin. Olfactomedins seem to occur in various tissues other than the nose and mediate responses to chemicals.
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Oh right! I didn't make that connection thanks.
 
Jonathan Edwards said:
OK, but since we know that people are very unreliable about attributing cause and that many are suggestible to physicians proposed explanations, and chemical exposure is a pretty loaded word, I think it remains pretty shaky as diagnostic category.
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I agree that we are prone to attributing causality to a lot of things.

The criteria try to get around that by requiring that (1) the symptoms are reproducible with [repeated] chemical exposure, and that (4) the symptoms improve or resolve when the incitants are removed.

Although there is the issue of blinding, especially for things that smell or are only present at specific locations or timepoints. And how quick is the onset and resolution?

I think someone with ME/CFS would fit those criteria. I don’t really tolerate anything that smells, which quite a lot of chemicals do. But my symptoms would be in the form of PEM so it’s not really the same.

Would someone with diabetes fit the criteria for example?
 
Utsikt said:
I think someone with ME/CFS would fit those criteria. I don’t really tolerate anything that smells, which quite a lot of chemicals do. But my symptoms would be in the form of PEM so it’s not really the same.
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Surely PEM would do fine for 'non-specific symptoms in more than one system'?

I don't think people with diabetes would fit.
 
Utsikt said:
I don’t really tolerate anything that smells, which quite a lot of chemicals do. But my symptoms would be in the form of PEM so it’s not really the same.
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Same including strong food smells or smoke. But since my decline to severe (or possibly my first covid infection) I have become allergic to my old beard oil in like a throat closing up and wheezing a bit when I put it on kind of way. Which is kind of different imo to the way I react to strong fragrance or the smell of dinner burning. MCS seems to cover both kinds.

A shame because it was really good beard oil!
 
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