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Multiple Chemical Sensitivity (MCS)




Multiple Chemical Sensitivity (MCS) PatientMatthew Hogg BSc (Hons) mFNTP mNNA mABH mABNLP
Registered Nutritionist, Hypnotherapist & NLP Practitioner

An Overview

Multiple Chemical Sensitivity is the name given to a syndrome in which a sufferer experiences multiple symptoms upon exposure to minute amounts of everyday chemicals. There is currently no officially recognized definition for Multiple Chemical Sensitivity. This is due to the fact that very little is known about it, especially the mechanisms involved with the onset of symptoms. Leading theories suggest a possible role for a hypersensitive central nervous system, immune dysfunction and impaired detoxification by liver enzymes. Some medical professionals, and even organizations, continue to insist that the syndrome is psychological in origin, even in the face of a growing amount of evidence from studies that show clear abnormalities in people with MCS on exposure to normally safe levels of chemicals. Through 1999 there were a total of 618 scientific articles, editorials, books, book chapters and reports relating to MCS. Of these, 308 supported an organic/physiological basis for symptoms whereas only 137 supported a psychological interpretation. (Source:

Although there is no definition universally accepted by the established medical institutions, Multiple Chemical Sensitivity experts (Bartha et al 1999) have come to a consensus on the criteria for diagnosis, and thus far these criteria remain unrefuted in the published literature. These criteria are as follows:

  • The symptoms are reproducible with [repeated chemical] exposure.
  • The condition is chronic.
  • Low levels of exposure [lower than previously or commonly tolerated] result in manifestations of the syndrome.
  • The symptoms improve or resolve when the incitants are removed.
  • Responses occur to multiple chemically unrelated substances.
  • Symptoms involve multiple organ systems [Added in 1999].

It's reasonable to expect that these criteria will be officially adopted in a form very close to the above in the relatively near future.

To complicate matters, however, a number of influential medical institutions, such as the American Academy of Allergy Asthma and Immunology (AAAAI), have renamed the illness as 'Idiopathic Environmental Intolerance' (IEI). They cite the reason for this to be the fact that no immune system involvement has been proven thus far and since "sensitivity" in medical jargon technically refers to an immune reaction, they deem MCS to be inaccurate. For the general population "sensitivity" and "intolerance" generally mean the same thing and MCS is so well known that most people are sticking with this name for now.



Many MCS sufferers can trace the start of their illness to an acute exposure to highly toxic chemicals (Gulf War veterans, and farmers using pesticides for example). For other sufferers the illness develops over a long period of time most likely involving chronic low level exposure to chemical substances. Although MCS can occur on its own, a large number of sufferers also suffer from CFS, Fibromyalgia and other related disorders. This obviously points to the possibility that all these illnesses are part of the same underlying process and likely have common causes.

MCS is a chronic condition with the patient usually experiencing some level of unwellness all the time. However, patients have an acute reaction when exposed to minute amounts of the chemicals to which they are sensitive. Often the level of a chemical that triggers a reaction may be so low that the sufferer can't even smell it.

Common symptoms of MCS upon exposure:

  • Fatigue
  • Headaches
  • Disorientation
  • Dizziness and Faintness
  • Flu-like symptoms
  • Nausea
  • Irregular or Rapid Heartbeat
  • Muscle and Joint Pain
  • Gastrointestinal problems
  • Mood Disturbances - Depression/Anxiety/Irritability
  • Short-term Memory Problems
  • Asthma/Breathing Problems
  • Rashes

Most sufferers have a distinct reaction upon every exposure. It is common to first experience dizziness, disorientation, rapid heartbeat and mood changes followed by flu-like illness and muscle/joint aches. In severe cases, the flu-like illness and aching can persist for days.

View the very BEST Environmental Illness Videos!

1. Your Health is Governed by Your Environment | Prof. BM Hegde | TEDx Talk

2. Demystifying Multiple Chemical Sensitivity

3. Social Determinants of Health - An Introduction 





Reactions in MCS are triggered by a vast array of everyday chemicals from perfume to diesel exhaust. The common ingredients in most of these chemical products are hydrocarbon based volatile organic chemicals (VOC's). Phenols (containing benzene) are commonly implicated. With everyday cosmetic and household chemical products, it is generally the addition of perfume that makes them bad news for MCS sufferers. Typically a sufferer will notice a sensitivity to one or two things to start with, perfume and cigarette smoke for example, and then will rapidly become sensitized to more and more chemical sources over a relatively short period of time. The reasons for this common occurrence are unknown but it is clearly something that needs to be investigated.

Common chemical triggers in MCS:

Pesticides - When the onset of MCS is a sudden event in an otherwise healthy person, acute exposure to pesticides is often reported as being the initial trigger. This is not surprising as these potent chemicals, many of which are chemically related to war time nerve agents, have multiple negative effects on the nervous, endocrine and immune systems. By their very nature, they are designed to exert these effects in order to kill pests. It is naive to think that these chemicals will not also damage these systems in humans, even in small amounts. Dr. Sherry Rogers, a respected expert on MCS and environmental illness, believes pesticides are the no.1 culprit when it comes to chemicals damaging human health. Common classes of pesticide include the organophosphates and organochlorides. Organochloride pesticides include DDT, chlordane, lindane and dieldrin. Some of the most potent, such as DDT, are now banned in most western countries but legal pesticides are still very damaging to health. Pesticides are virtually inescapable, being used on lawns, crop fields, roadside weed control and even indoors as pest control. Ever stopped to think what's in flea collars and flea killing products you use on your pets?

Perfume - According to a 1986 report by the Committee on Science & Technology, U.S. House of Representatives, 95% of chemicals in perfumes and fragranced products are synthetic chemicals derived from petroleum. Some of the major perfume ingredients include benzaldehyde, benzyl acetate, benzyl alcohol, camphor, ethanol, ethyl acetate, limonene, linalool, a-pinene, g-terpinene and a-terpineol. All of these chemicals are known to have negative health consequences, mainly due to effects on the central nervous system.

Gasoline - Vapours cause central nervous system depression. In healthy individuals, high level exposure leads to symptoms such as eye and respitory irritation, dizziness, headache, drowsiness and incoordination.

Vehicle Exhaust - Despite attempts in recent years to reduce pollution from vehicle exhausts, there is no getting away from the fact that burning petroleum products produces undesirable chemical byproducts. Some of the major chemicals in vehicle exhaust fumes include carbon monoxide, nitrogen dioxide, sulphur dioxide, benzene, formaldehyde, polycyclic hydrocarbons and suspended particles, including PM-10 (particles less than 10 microns in size - visible only with a good dissecting microscope). Even in otherwise healthy individuals, these chemicals are known to cause a wide range of symptoms. In the chemically sensitive, benzene, formaldehyde and polycyclic hydrocarbons are known to be particularly likely to trigger symptoms.

Household Cleaning Products - The Environmental Protection Agency (EPA) in the US states that the air in the average home may be up to 5 times as polluted as the air outside. Much of this pollution comes from the use of common household cleaning products. They also caution that of the many thousands of chemicals in use only around 3 in 10 have actually been safety tested. Examples of common chemicals in cleaning products include diethyl phthalate, found in a range of products, toluene, found in stain removers, and hexane/xylene, found in aerosol sprays. Diethyl Phthalate is a known endocrine disrupter (interferes with hormone activity), toluene is a known carcinogen (cancer causing agent) and can cause neurological problems, and finally both hexane and xylene can also damage the nervous system.

Other cleaning products that commonly trigger MCS symptoms include dishwasher detergent, laundry liquid/powder, fabric softener, air "fresheners", and bathroom/kitchen detergents. Highly fragranced products are always likely to be the most troublesome.

Personal Care Products & Cosmetics - An equally important contributors to indoor air pollution are the many personal care and cosmetic products that fill bathroom cabinets etc. The added danger with many of these, such as hair spray and deodorant, is that we carry the chemicals around with us all day on our bodies. Some of the common chemicals found in such products include cocoamide DEA (detergent in most shampoos, moisturizers and more), propylene glycol (in deodorant, shampoos, shaving gels, moisturizers and more), sodium lauryl sulfate (detergents- in shampoos, toothpastes, more), acetone (nail varnish remover) and benzaldehyde (hair spray, deodorant, shaving foam, shampoo, bar soap and more).

Other problem products include shower gels and liquid soaps, nail varnish, hair styling products, hair conditioners, sun lotion, and scented bath products. Again the highly fragranced products tend to be the most troublesome to the multiple chemical sensitivity patient.

Cigarette Smoke - Often one of the initial symptom triggers when someone becomes chemically sensitive, probably due to the large amounts of volatile petrochemicals released into the air, particularly aldehydes. Until recently, when smoking bans became more widespread, it was very difficult for MCS sufferers to avoid. Amongst other things, cigarette smoke contains ammonia, acetaldehyde, acetone, benzene, butyraldehyde, carbon monoxide, formaldehyde, hydrogen cyanide, nitric oxide and toluene. Ammonia is an irritant to mucous membranes and can trigger asthma. It also has numerous central nervous system effects, as do all the hydrocarbon chemicals including the aldehydes, benzene derivatives and toluene. These hydrocarbons are strongly implicated in most theories of how MCS occurs, particularly the 'Limbic Sensitization' hypothesis (see below). Elevated levels of nitric oxide (NO) are thought to play a major role in chemical sensitivity by a number of researchers, specifically Dr. Martin Pall, who is himself chemically sensitive.

Natural gas - Exposure to natural gas will occur at home for most people, if it is used in heating systems, stoves, water heaters etc. exposure at work may be common for someone working in industries that involve pulp and paper, metals, chemicals, petroleum refining, stone, clay, glass, plastic, and food processing. When burned, natural gas produces hydrocarbon products, primarily methane, along with carbon dioxide and smaller amounts of carbon monoxide.

New carpet - Most new carpets contain a cocktail of volatile organic compounds (VOC's) as ingredients in glues, backing materials, flame retardants, dyes etc. These include many of the chemicals we are now familiar with, such as acetone, toluene, xylene, formaldehyde, and benzene derivatives. When the carpet is new these chemicals "off gas" over a period of around 6 months to 2 years, polluting the air in the home.

Particle board - Manufactured particle board is now used much more widely than solid wood in our homes, in such things as fitted kitchens, furniture such as shelving, bookcases, cabinets (especially flat-pack) and laminate flooring. Particle board is basically wood chip bound together by chemical adhesives into solid boards. As with new carpets, new particle board products off gas VOC's over a relatively long period of time and will trigger symptoms in the chemically sensitive and may induce sensitivity in previously healthy individuals. Chemicals that off gas from particle board are similar to those from carpets with formaldehyde most often the main offender.


Other common triggers:

The above is by no means an exhaustive list. Here are some other common triggers of symptoms in MCS patients:

  • marker pens
  • soft plastics
  • new clothes
  • new furniture
  • newspapers/magazines
  • paint
  • varnish
  • solvents
  • glues/adhesives.....and more

In addition to these VOC's that cause a reaction when inhaled, some sufferers also complain of symptoms when they ingest certain things. These include:

  • Food Additives
  • Food Preservatives
  • Medications
  • Unfiltered Water


The Impact of Multiple Chemical Sensitivity on Quality of Life

Multiple chemical sensitivity is a devastating illness, not just because of the distress caused by the symptoms themselves, but also from the resulting effects on all areas of life. An MCS sufferer typically becomes more and more isolated and withdrawn as they simply can't be around people (wearing perfume, deodorant etc) or in public spaces where chemicals are routinely used. MCS sufferers often lose their jobs as they can't tolerate the chemicals in the work environment, and relationships often break down as the partner is unable to understand or adapt to living without the use of common chemical products. To add insult to injury, because of the current medical confusion over the illness, patients often have to endure being labeled as attention seekers or hypochondriacs, as well as having to fight, often in court, to be granted disability benefits and appropriate housing.


Research Findings

Although the amount of medical research into MCS is still a lot lower than would be desirable, a relatively high number of studies have discovered consistent abnormalities in MCS patients and also been able to show convincing evidence of possible mechanisms in animal and other laboratory models.


Limbic Sensitization or "Kindling"

One common finding is that a part of the brain known as the 'limbic system', which has strong connections to the part of the brain involved with our sense of smell, the olfactory system, shows increased electrical activity in MCS patients when exposed to chemicals they are sensitive to. One of the main functions of the limbic system is the regulation of mood and autonomic nervous system functions, which would explain why many symptoms of MCS involve changes in mood, thought and sensory information. As a result of these findings a number of researchers have suggested that in MCS, the brain, and limbic system in particular, has become hypersensitized so that smaller amounts of chemicals cause the brain to become activated (1 , 2). This theory has been given a lot of weight by further research that has shown the limbic systems of animals exposed to either short term high concentrations of chemicals (such as formaldehyde), or long term lower concentrations, have become hypersensitized so that further exposure to a concentration of chemical, that previously would have had no effect, now initiates a high amount of electrical activity in their limbic systems (3 , 4). Researchers found that chemicals that differed greatly in their structure, had a remarkably similar effect on the limbic system. Additionally, the hypothalamus is part of the limbic system and is an important information processing centre and is the focal point in the brain where the immune, autonomic nervous, and endocrine systems interact. It has long been proposed that a malfunctioning hypothalamus upon exposure to chemical triggers could produce the symptoms described in MCS through its influence on all these body systems. The limbic system is known to be responsive to both chemical and cortical stimuli. This means that it can be activated either by thought, or exposure to chemicals in the form of natural neurotransmitters, or more importantly in the context of multiple chemical sensitivity, in the form of chemical irritants that enter the body through the nose. This fact provides a strong argument against those who state that MCS is purely a psychological illness, as chemicals triggering activation of the limbic system could initiate mood changes and other symptoms typically labeled as psychiatric.

The sensitization, or loss of tolerance, explanation is the main point behind the Toxicant Induced Loss of Tolerance (TILT) theory put forward by chemical sensitivity researcher Dr. Claudia Miller.


Abnormal Regional Cerebral Blood Flow
Another brain abnormality found is abnormal regional cerebral blood flow (rCBF). In MCS sufferers, blood flow to certain areas of the brain may be reduced or abnormally chronically, and be further reduced or altered after exposure to an offending chemical. This is an interesting finding because reduced brain blood flow has also been documented in CFS and Fibromyalgia. The link below shows SPECT brain scans of a woman MCS sufferer before and after exposure to perfume along with explanation of the results from the lab.

SPECT Brain scan of MCS sufferer


The porphyrias are a group of rare diseases that occur due to deficiencies of enzymes used in the process that forms heme. Heme is the important iron containing protein in blood used in oxygen transport and also in a group of detoxification enzymes in the liver known as cytochrome P450. Porphyrins are the intermediate chemicals in the formation of heme and it is the build up of porphyrins in different tissues, as well as the loss of ability to detoxify certain chemicals, that causes the symptoms of the illnesses. The symptoms present in an individual depend upon which enzymes are deficient and may include intolerance's to drugs and chemicals, abdominal and musculoskeletal pain, photosensitivity resulting in multiple skin problems, fatigue, neuropsychological problems, psychiatric problems and pink/purple urine (due to increased porphyrin content). Porphyrias usually occur in acute episode triggered by medications, menstrual periods, malnutrition or other illness, at other times the sufferer may show no symptoms and normal porphyrin levels. Due to the similarity of symptoms between these illnesses and MCS, a number of researchers decided to test MCS patients for increased porphyrin content in urine and stool samples. One study found that 60-90% of MCS patients tested showed porphyrin abnormalities. Other findings come from a doctor who had a number of patients describing pink/purple urine. When tested a significant number had higher than normal levels in urine and stool samples. The abnormalities however have been less marked than in the traditional porphyrin illnesses. More research is definitely needed in this area to further substantiate abnormalities.


Increased Nitric Oxide
Dr. Martin Pall has done a lot of research into levels of nitric oxide and its derivatives, such as peroxynitrite. Nitric oxide (NO) is a secondary messenger molecule in the brain, used by cells to communicate. Dr. Pall feels that there is convincing evidence that elevated levels of NO in MCS patients brains is a key factor in the illness. He cites the following reasons for this conclusion:

Several organic solvents thought to be able to induce MCS, formaldehyde, benzene, carbon tetrachloride and certain organochlorine pesticides all induce increases in nitric oxide levels.

A sequence of action of organophosphate and carbamate insecticides is suggested, whereby they may induce MCS by inactivating acetylcholinesterase and thus produce increased stimulation of muscarinic receptors which are known to produce increases in nitric oxide.

Evidence for induction of inflammatory cytokines by organic solvents, which induce the inducible nitric oxide synthase (iNOS). Elevated cytokines are an integral part of a proposed feedback mechanism of the elevated nitric oxide/peroxynitrite theory.

Neopterin, a marker of the induction of the iNOS, is reported to be elevated in MCS.

Increased oxidative stress has been reported in MCS and also antioxidant therapy may produce improvements in symptoms, as expected if the levels of the oxidant peroxynitrite are elevated.

In a series of studies of a mouse model of MCS, involving partial kindling and kindling, both excessive NMDA activity and excessive nitric oxide synthesis were convincingly shown to be required to produce the characteristic biological response.

The symptoms exacerbated on chemical exposure are very similar to the chronic symptoms of CFS (1) and these may be explained by several known properties of nitric oxide, peroxynitrite and inflammatory cytokines, each of which have a role in the proposed mechanism.

These conditions (CFS, MCS, FM and PTSD) are often treated through intramuscular injections of vitamin B-12 and B-12 in the form of hydroxocobalamin is a potent nitric oxide scavenger, both in vitro and in vivo.

Peroxynitrite is known to induce increased permeabilization of the blood brain barrier and such increased permeabilization is reported in a rat model of MCS.

5 types of evidence implicate excessive NMDA activity in MCS, an activity known to increase nitric oxide and peroxynitrite levels.

Dr. Pall feels that the resulting effects of too much NO in the brain could result in the symptoms reported by MCS sufferers through various pathways resulting from overactivation of the brain. He concedes however, that this does not explain how people become sensitive to chemicals in the first place. For an explanation for this he postulates that combining his work with elevated NO, with the limbic sensitization theory, a 'fusion theory' of all aspects of MCS can be produced.

Read more about this in Dr. Pall's article - Multiple Chemical Sensitivity - The End of Controversy


Other Areas of Research

Immune System

A number of studies have been conducted with MCS sufferers regarding immune function but the findings have not always been consistent. A couple of studies have found abnormal T and B-lymphocyte numbers and activity and increased autoantibodies, that is antibodies that react with the bodies own tissues. Some data has shown a low T-helper/Suppressor ratio which would act to impair immune function. Probably the most consistent finding is that of low natural killer (NK) cell activity. This is interesting in the light of strong evidence for low NK activity in chronic fatigue syndrome and fibromyalgia. The inconsistent findings have been suggested to be the result of changes in immune activation over time following an exposure, with the resulting difficulties in testing MCS patients appropriately in research studies. How the above findings would cause the myriad symptoms of MCS is far from clear but immune dysfunction remains a popular theory for the mechanism of the illness.


Impaired Detoxification/Low Glutathione
Another abnormality in MCS is impaired detoxification of xenobiotic chemicals (chemicals foreign to the body). It has been found that the ability to detoxify these chemicals varies widely in the general population but so far MCS patients have not been meaningfully studied with regards to this. There are now a few researchers looking at the metabolism of chemicals in MCS and given the connection with Porphyria discussed above and the role of detoxification potential in that group of illnesses, it would seem an area that needs a lot more attention. It has been found however that MCS patients exhibit lower than normal levels of glutathione, the body's major detoxification chemical, that is also characteristic of chronic fatigue syndrome, fibromyalgia, gulf war syndrome and autism. Low glutathione would result in poor detoxification and excretion of toxic chemicals, leaving them in the blood stream and tissues where they could cause cellular damage and interfere with biochemical processes.

For a review of further abnormalities in MCS see Biomarkers of MCS - Abnormal Medical Tests and Physical Signs Associated with Multiple Chemical Sensitivity


What do we know about common chemicals and health?

The simplest answer to this is...not much.

Since World War 2 the production of synthetic organic chemicals has skyrocketed. In 1945, total production of these chemicals was under 10 million tons compared to 110 million tons today(1).

A total of 4 million chemical compounds were described in the scientific literature between 1965 and 1989. Of the 60,000 chemicals in wide use in most western countries in 1989 only around 2% (1200) had been comprehensively examined by scientists. There is no research data at all available on about 50,000 commonly used chemical substances(2).

A UK academic recently recommended a program to rapidly test and catalogue 30,000 chemicals within the next 5 years. Chemicals found to cause health problems would then be subjected to more intensive longer term testing. This would certainly be a step in the right direction.


Related Conditions:

Electrical Hypersensitivity causes sufferers to develop multiple symptoms when exposed to electromagnetic fields from such things as electrical equipment, wiring and power lines. Multiple chemical sensitivity sufferers may be more likely to also suffer from electrical hypersensitivity.

Sick Building Syndrome involves a group of people becoming ill whenever they enter a particular building such as an office. Many factors can contribute to symptoms including both biological and chemical pollutants.




Multiple Chemical Sensitivity (MCS) Forums

View the very BEST Environmental Illness Videos!

1. Your Health is Governed by Your Environment | Prof. BM Hegde | TEDx Talk

2. Demystifying Multiple Chemical Sensitivity

3. Social Determinants of Health - An Introduction 



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