Multiple Chemical Sensitivity, MCS

4 Examples of MCS

4.1 MCS after exposure to organic solvents
     4.1.1 MCS in workers after acute exposure to gasoline fumes during
     tunnel construction work

     4.1.2 MCS after exposure to plastics
4.2 MCS after exposure to pesticides
     4.2.1 The situation in Denmark
4.3 Wood preservatives - pentachlorophenol (PCP) in Germany
     4.3.1 MCS after exposure to Rentolin in Denmark
4.4 MCS in relation to indoor climate
4.5 The Gulf War Syndrome (GWS)
4.7 Chemicals which can cause MCS
     4.7.1 Chemicals and initial exposure in connection with MCS
     4.7.2 Chemicals which cause multiple reactions (trigger substances)

In this chapter, typical examples of cases of MCS that fulfil the definition criteria and progress in two phases, as mentioned in chapter 2, are described:

  • A perceived initial exposure to a chemical in a major though not necessarily toxic dose
  • A state with increased response from several organs to exposure to the same chemical in a lower dose and the development of symptoms in connection with exposure to other chemicals (trigger substances)

4.1 MCS after exposure to organic solvents

It is well known that exposure over many years to organic solvents can cause various injuries to the brain and other organs. It seems possible that MCS can also be caused by such exposure over a long period of time.

A report from the Clinic for Occupational Medicine and the Department of Oto-rhino-laryngology at the Copenhagen University HospitalNational Hospital of Denmark (Rigshospitalet) (Gyntelberg, 1986) is one of the first publications dealing with such cases.

The author used the term “Acquired intolerance for organic solvents”. The investigation involved 50 persons who had developed a number of symptoms from different organs after exposure to low doses of solvents. These doses had not previously created symptoms. All persons had previously experienced acute solvent poisoning. 22 demonstrated toxic encephalopathy.

The most apparent symptoms in all persons were dizziness, nausea, and fatigue, which disappeared when the solvent was removed. There is no mention of symptoms from exposure to other substances. Because of the absence of this information, Gyntelberg's report does not comply with the definition of MCS.

The authors also mention that Stockholm and Cohr (1979) found that persons who had previously experienced solvent poisoning were more sensitive to solvents than other research subjects, during climate chamber experiments.

Rasmussen (2002) has confirmed that persons with nervous system damages, e.g., toxic encephalopathy, have enhanced sensitivity to organic solvents and often also to non-neurotoxic chemicals.

Occupational physicians in Sweden have had similar experiences (e.g., Ørbæk, 1998; Lindelöf and Georgellis 1999, 2000) and Levy (1997) in Norway mentions that the second phase of MCS is often triggered after a long period of interruption of work and exposure. When these persons return to work, they can no longer endure exposure to chemicals, which they were previously used to. Nor can they endure them in lower concentrations. They begin to complain of diffuse symptoms when exposed to perfumes, exhaust gasses and the like. The same persons can also experience lowered tolerance towards alcohol and medicine.

An MCS-like syndrome was described in an occupational medicine investigation in France “Syndrome d'intolérance aux odeurs chimiques” (intolerance syndrome for chemical odours). In 19 out of 30 cases the symptoms were caused exclusively by exposure to organic solvents, corresponding to Gyntelberg's description (Grimmer, 1995). A sub-group of 17 out of the 30 later developed intolerance towards other substances. This phenomenon was called “hypersensibilité olfactive” (odour hypersensitivity). Not all of the 17 had previously been exposed to solvents.

A group from the Division of Environmental Medicine in Stockholm found that housepainters more than any other occupational group, suffered from MCS-like symptoms. In a questionnaire survey among active painters, 191 out of 584 respondents complained of odour sensitivity towards organic solvents, while 49 had symptoms fulfilling the criteria of MCS. The latter group of painters were clearly more bothered by their symptoms than the remainder (Lindeløf, 2000) (See also section 6.4).

Cones (1987) and Lax (1995) both describe a small group of persons with MCS among their occupational medicine patient groups consisting of 1200 and 605 referred patients respectively. 13 of Cone's and 35 of Lax's patients fulfilled Cullen's criteria. Most of Cone's patients had been exposed to organic solvents in the initial phase.

Table 4.1 Overview of MCS cases involving exposure to solvents (occupational medicine investigation)

Author Syndrome Number of
initial "trigger" phase
Gyntelberg, 1986 Acquired intolerance to solvents 50 50 organic solvents Organic solvents
Grimmer, 1994 Chemical odour intolerance syndrome
Olfactory hypersensitivity

19 organic solvents Organic solvents

And a “wide range” of other chemicals
Lindelöf, 2000 Odour sensitivity
Organic solvents
Organic solvents
Organic solvents
"a wide range"
Cone, 1987 MCS 13 11 organic solvents "a wide range"
Lax, 1995 MCS 35 Not indicated "a wide range"

4.1.1 MCS in workers after acute exposure to gasoline fumes during tunnel construction work

Davidoff (1998) tells of 77 unskilled construction workers who were exposed to chemical fumes from earth polluted by gasoline from a service station, during a period of two months when they were digging a tunnel. Not before two months after having noticed the smell of gasoline for the first time, did the workers start complaining of headaches, dizziness, irritation of eyes and throat, and coughing. Benzene concentrations of 60 ppm were measured in the tunnel air (Dräger tubes). The work was then stopped and the tunnel closed. More reliable measurements of all chemical fumes in the tunnel were not performed.

30 randomly chosen persons were examined twice: shortly after the episode and 10-13 months later, when 10 workers had developed symptoms fulfilling the MCS criteria. Two of these had previously been subjected to chemical fumes, while the other eight had not experienced symptoms prior to the tunnel episode (26,7% of the 30 tunnel workers examined).

The tunnel workers experienced symptoms less frequently (at least once a week) and for shorter periods of time than another group of MCS patients. But the symptoms were similar and from several organs such as the central nervous system, the respiratory tract, muscles, ligaments and joints, and the gastrointestinal tract.

The symptoms had not forced any of the workers to resign their jobs. Most of them were still working, when they were examined the second time.

This cohort of workers is rather unusual in an MCS context, since none of them knew anything about MCS, when they experienced their first symptoms. They have not been examined by clinical ecologists or had contact with the patient association for MCS victims, since then.

The investigation is interesting because it involves an almost experiment-like exposure situation where only some of the persons, who had previously been exposed and had been acutely poisoned, developed MCS.

4.1.2 MCS after exposure to plastics

50-75 workers at an airplane factory in the US became acutely ill, when a new plastic product was introduced. The symptoms resembled the ones known from acute solvent poisoning. The product was found to contain phenol, formaldehyde, and methylethylketone, which were measured inside the factory in concentrations below the limit value. Twelve workers complained of persistent symptoms due to various odours experienced in the everyday environment. A panel of experts examined them and found no other illnesses to explain their symptoms (Simon, 1990).

4.2 MCS after exposure to pesticides

According to Ashford and Miller (1998), exposures to organophosphate and carbamate pesticides have been emphasized as possible causes of MCS in several investigations. The course of events is typically an acute poisoning, sometimes accompanied by chronic symptoms of poisoning from the central nervous system and later development of diffuse symptoms from several organs, corresponding to the definition of MCS.

According to the patient association for MCS victims in the US, 80% of the 6800 members have stated that they know when, how and due to which substances they became ill. 60% became ill initially after exposure to pesticides (Ashford & Miller, 1998).

Tabbershaw (1966) reported on 114 farmhands in California with acute organo-phosphate poisoning. Some of these later developed an MCS-like condition. Three years after having been poisoned, 22 persons complained of indisposition when in contact with pesticides and organic solvents. Six persons quit their job due to symptoms. The others tried to avoid pesticides in their work. 61 persons from the original cohort could not be traced and it is uncertain how many of these had moved away from the area due to MCS.

Cone (1992) describes an episode where 250 guests at a hotel were exposed to propoxur, a carbamate insecticide used against cockroaches, on several occasions. Many guests had momentary acute symptoms of poisoning, while 19 complained of persistent symptoms. They were examined at a clinic for occupational medicine some 5 to 15 months after the episode. Twelve of them complained of hypersensitivity to odours from perfumes, gasoline, printing ink in newspapers, various detergents, pesticides, and solvent-based products, which had not bothered them before the stay at the hotel.

Pesticide poisonings in eight countries (DK, S, N, UK, D, B, NL, GR), most of which occurred in working environments, are described in the EU report (1994).

Eight out of 23 persons in Germany with acute pyrethroide poisoning later developed MCS symptoms corresponding to Cullen's criteria. Clinical examinations and laboratory tests of these persons were normal (European report, 1994).

4.2.1 The situation in Denmark

Several cases of acute pesticide poisoning in gardeners and others have been reported from Denmark (Lander, 2000). No systematic investigations to show whether or not the victims fulfil the MCS criteria have been performed. According to Lander, a small group is bothered by odours, when they spray in the greenhouses. The cause of symptoms is ascribed to aromatic warning substances, which have been added to the pesticide (Lander, pers. Com., 2001).

As opposed to the situation in the US, where pesticides are the most frequently mentioned group of chemicals in connection with MCS, Danes do not use pesticides privately very often, and then mostly out-of-doors.

4.3 Wood preservatives – pentachlorophenol (PCP) in Germany

In connection with the European investigation, German experts reported on many cases of an MCS-like syndrome, primarily due to pentachlorophenol. This chemical was used on wood indoors and contained a complex mixture of substances such as dioxin, furan and organic solvents. 10,000 cases of poisoning (acute and chronic) have been reported. 100 of these were from children's institutions and schools.

The course of some of the cases fulfils the MCS definition with initial exposure to a substance followed by various non-specific complaints after exposure to quite low concentrations of various chemicals. A court in Frankfurt found it very probable that pentachlorophenol caused the MCS complaints in a group of people. The manufacturer appealed the court decision but the outcome of the appeal case is not known (European report, 1994).

There are similar reports from other countries. High indoor concentrations of pentachlorophenol were measured in three towns in The Netherlands, where inhabitants complained of symptoms. But a connection between the symptoms and the substance could not be documented (European report, 1994).

In Belgium, the term PCP-Syndrome was used to describe a condition caused by the use of pentachlorophenol. Experts found many people with symptoms corresponding to MCS. They were interpreted as a form of intolerance rather than classical poisoning (European report, 1994).

4.3.1 MCS after exposure to Rentolin in Denmark

Rentolin is a wood preservative, which has been used indoors, by mistake. This product is only meant for use out-of-doors. But the importer advertised that it could be used for ceilings, floors and kitchen tables.

The product consists primarily of solvents (white spiritturpentine), linseed oils, and a fungicide (dichlofluanid).

For a period, many private individuals who had used Rentolin in their homes issued complaints. Several of these persons had been examined in occupational medicine clinics, where a pathological picture resembling MCS, with symptoms from the central nervous system and several other organs, was disclosed. Many of the cases were diagnosed as cases of acute poisoning by solvents, whereas the occupational medicine physicians could not document a connection between the use of Rentolin for the preservation of wood and the chronic MCS symptoms (Viskum, 1999). A toxicological assessment does, however, make a connection likely, especially if Rentolin is used extensively.

Subsequently, the Danish EPA has forbidden the use of Rentolin indoors, due to its high content of dangerous solvents.

Based on assessments by two experts on environmental medicine and indoor climate, a Danish court has ruled that Rentolin could be the direct cause of the MCS symptoms of the plaintiff. The experts were of the opinion that the dichlofluanid content, could have been of decisive importance.

4.4 MCS in relation to indoor climate

As mentioned in chapter 2, symptoms due to indoor climate can have many causes, which do not necessarily have anything in common with MCS. This section focuses on chemicals that can cause MCS-like symptoms.

These chemicals, which can be traced in indoor air and originate from various indoor sources, can collectively be termed volatile organic compounds (VOC). Wolkoff (1995) distinguishes between the following main sources:

  • Construction materials, paint, glue, wallpaper, furniture, carpets, etc.
  • Materials from human activities: Office machines, household machines, personal care, etc.
  • Micro-organisms: mould fungi, etc.
  • Out-of-doors air pollution from traffic and industry
    (see also section 4.8).

US literature contains many accounts from persons with MCS, whose symptoms started when they got a new office, moved into a new house, or had a new carpet laid. In most cases these persons worked in large office spaces with many employees , where 2-300 square meters of new carpet were laid. The carpet was glued to the floor with glue containing styrene and butadiene, which was put on the polymerised undersides of the carpet (Ashford & Miller, 1998).

Many more chemicals are used in private homes in the US than in Europe. For large parts of the population this can lead to greater indoor exposure to chemicals than in Denmark/Europe.

4.5 The Gulf War Syndrome (GWS)

In connection with previous wars (Vietnam, Korea), a limited number of soldiers were troubled by symptoms, some of which resembled MCS, after returning home. While these cases were previously assessed as being related chiefly to psychogenic traumas, other hypotheses are now being tested.

The large group of soldiers with health complaints after the Gulf War have led to large clinical investigations in the US and Great Britain. Several research projects are still running.

One of the many hypotheses for the cause of GWS is exposure to various chemicals (pesticides, vaccines, antibodies against poisonous gases, etc.), which the soldiers were exposed to through inhalation or by injection. Some of the veterans with GWS may possibly fulfil the criteria for MCS, which means that they were exposed to an initial chemical poisoning by inhalation and since then developed various symptoms, when coming into contact with odours (see also remarks in section 2.3).

The Danish Gulf War Study did not disclose any exposures to chemicals before and during the Gulf War (Ishoy, 1999).


Due to a general lack of awareness of and interest in MCS in Europe and especially in Denmark not all of the variants of MCS-like cases, which might have occurred, are known.

By far, most of the cases are known from occupational medicine investigations, and they mostly have to do with exposure to solvents or pesticides. Two younger persons with MCS were employed in Danish public swimming baths. Chlorine fumes, which are formed under special circumstances, caused these symptoms (e.g., trihalomethanes and chloramines). Both had to leave their job and be re-educated (Raffn, pers. com., 2001).

Graveling wonders why he finds that the people who work the most with chemicals and, therefore, should be the ones being exposed the most, have MCS less often. This remark does not correspond to the experience in Denmark, where most of the assumed MCS cases are linked to occupations where people have previously been exposed to solvents, and a few other occupations such as gardening and hairdressing, etc.

Graveling does not mention his experience with, e.g., occupationally exposed cases. It is remarkable that Graveling and his co-authors, all of which are employed at an institute for occupational medicine, do not give figures for occupation-related MCS cases in Scotland and England. After all, the British Health and Safety Executive (HSE) commissioned their report (Graveling, 1999)(see chapter 3).

The cases involving the wood preservative Rentolin, which were mentioned above, are good examples of the few sporadic cases known from private homes.

4.7 Chemicals which can cause MCS

4.7.1 Chemicals and initial exposure in connection with MCS

The following chemicals have been mentioned in connection with MCS and initial exposure: All types of organic solvents (occupational or private), pesticides (organophosphates and carbamates), hair-care products (hairdressers) and substances containing chlorine (e.g. public swimming baths).

Table 4.2 from the EU report lists statements of experts from the different countries regarding chemicals that are presumed to cause MCS. Organic solvents and pesticides are most frequently mentioned.

The basis forWhy the Danish experts reporting are of the opinion that stress and psychosocial factors can elicit MCS (table 4.2 bottom) is unclear. These factors are not among the most well-known factors of initial exposure (see also subsection 2.2.2).

Table 4.2 Possible factors to elicit MCS (initial exposure). Information from nine countries in a European investigation (European report, 1994)

Exposure factor DK S N SF D NL B UK GR
Amalgam / Mercury   + +   +        
Anaesthesia gasses                 +
Carpets and glue   +       +      
Diesel exhaust +                
Formaldehyde +   +   +       +
Hair-care chemicals + +             +
Indoor climate + +   +          
Degreasing agents +                
Methylmethacrylate   + +            
New, renovated buildings   + +   +        
Organic solvents + + + + + + + + +
Paint, lacquers + +     +       +
Pentachlorophenol, etc.         + + +    
Pesticides +   +   +   + + +
Drugs     +           +
Printing materials + +              
Stress – psychosocial factors + +     +     +  

4.7.2 Chemicals which cause multiple reactions (trigger substances)

Table 4.3 lists a wide, up-to-date variety of chemicals according to newer Danish information and literature from the US. The chemicals listed can be found indoors as well as out-of-doors at work, in public places, and in private homes.

"Indoor VOC, others" covers chemical fumes found nowhere else in the table. Wolkoff (1955) gives a detailed description of both the different causes of VOC and the large number of detectable organic substances (see also section 4.4). The range of VOC smell/odour concentrations includes many orders of magnitude (from mg/m³ to g/m³ or even lower).

A number of exposures contribute to a complex type of air pollution involving combined effects from several chemicals and from chemicals and other factors.

Table 4.3 List of the most frequently reported triggering chemicals (i.e., Miller, 2001)

• Organophosphates, carbamates
• Organic solvents
• Paint, lacquers, varnish
• Glue
• Metal cleaning
• Printing ink and cleansing
• Household chemicals
• Nail polish remover
Wood preservatives
Dry cleaning
Tobacco smoke
Frying odour
Chlorine fumes (public swimming baths)
Hair-care products (Ammonium compound)
Automobile exhaust gasses
Fumes from newly laid carpets
Perfume, eau de cologne
“Fresh-air” spray
Scents in soap, washing powder and other household products
Gasoline fumes
Indoor VOC, others

Reactive substances can react with other substances and in this way create new compounds with triggering capacity. E.g., ozone reacts with citrus oil, creating a compound with a strongly irritating odour. By adsorbing to, e.g., dust particles, poorly evaporating chemicals can trigger via dust exposure (Wolkoff, 1999).


Version 1.0 March 2005, © Danish Environmental Protection Agency