Last time (some years ago) I looked into studies about it, the most believable (by me) study did use some method to prevent detecting the chemicals via smell, and the subjects' ability to identify chemicals they claimed they were sensitive to vanished (equaled random guessing). I've yet to encounter a well-done study that did prove that MCS was real. Ditto for EMF sensitivity.
Prevalence of Multiple Chemical Sensitivity in Canada Between 2000 and 2020, 2026, Robins et al
- Thread starter forestglip
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Real? In what way would it not be a real disorder if it only happened when a person smelled the chemical?
For all we know, PEM is only triggered because of "knowing" that exertion is happening, and if someone in a coma artificially had their muscles stimulated, nothing may happen.
Jonathan Edwards
Senior Member (Voting Rights)
I think ME/CFS is a lot more than just PEM. In fact I think one could reasonably define the population with ME/CFS as conforming to a syndrome without any reference to PEM. PEM is an interesting aspect but I think it may be overemphasised.
I agree that MCS in the sense of a syndrome of feeling unwell consistently following smelling certain chemical substances will be real in that it will describe certain people (maybe all of us for ammonia and cadaverine). But whether there is a real syndrome out there in the sense of a cluster of symptoms that clearly point to some specific pathway I am doubtful.
Peter T
Senior Member (Voting Rights)
I think it is an interesting question as to whether chemical sensitivity involves smell or some other mechanism, but this is surely a discussion about mechanism rather than validity of the concept.
Personally in relation to my sensitivity to perfumed soap or similar the mechanism is definitely related to smell, as using it can trigger PEM only when I am aware of the smell but does not cause any skin irritation. However others have very different experiences. In contrast my gluten sensitivity happens regardless of whether I have any awareness of having consumed gluten, it is independent of any taste, texture or smell.
Defining multiple chemical sensitivity is not straight forward because we do not know the mechanisms of triggering any symptoms. Indeed individuals experiencing significant symptoms may experience multiple triggering mechanisms. I feel, like ME/CFS, we lack any good basic descriptive data, though perhaps we are a bit further ahead with ME/CFS.
MCS isn't about smelling chemicals, it's about biological responses to exposure to those chemicals. Your nose might not have a sensor for a specific chemical, but if the subject's symptoms correlated with the level of the chemical in the air, that would be real chemical sensitivity. That's where there's a lack of evidence for MCS.
In the case where a smell triggers a memory leading to a response, such as the smell of burning wood triggering memories of being trapped in a house fire, should that be considered MCS? It is a real response to a molecule, but it's a psychological response rather than a biological one. If the definition of MCS covers too many unrelated mechanisms, it's not a useful definition. Allergies and food intolerances and poisonings are responses to chemicals too.