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Multiple chemical sensitivity

Updated: Aug 21, 2021

Multiple chemical sensitivity (MCS) is an unrecognized serious chronic and devastating disease characterized by dysregulation of multiple organ systems causing a wide range of symptoms. It appears as result of a one-time major exposure, or a chronic low-level exposures to environmental chemicals and toxins from products such as solvents, pesticides, paints, building materials, tabaco smoke, vehicle exhaust, air fresheners, cleaning products, perfumes, and personal care products (Caress and Steinemann, 2004; Pall, 2009). Many of those substances emit volatile organic compounds (VOC) (Caress and Steinemann, 2004; Pall, 2009). The trigger can be also the poor indoor air quality of a moisture-damaged houses (Pall, 2009; Genuis, 2010). Besides its recognition since the 1940s, MCS remains controversial among doctors, researchers, legislators and regulatory agencies. The disease still lacks diagnostic tests and International Classification of Diseases code (ICD-10), but it can be set based on the following criteria:

  • the disease starts after chemical exposure

  • the disease is chronic, lasts more than 6 months and impairs patient’s quality of life

  • symptoms are present in several organ systems

  • symptoms appear frequently on chemical exposure

  • very low concentrations of the chemical (lower than the average tolerated and/or previously tolerated) may cause worsening of symptoms

  • the response occurs to many chemically diverse substances.


Patients with MCS will usually recover completely if exposure to symptomatic chemicals is stopped quickly. However, re-exposure to the same chemicals leads to chronic illness. Symptoms start to be present at the lower concentrations of chemicals. The disease interferes with daily life and work, and manifests in several organ systems including:

  • nervous system: headache, dizziness, intensification or loss of sense of smell, seeing and/or hearing difficulties

  • respiratory system: pain and burning feeling in the airways, chest pain, short of breath, cough, asthma, reactive airways dysfunction syndrome (RADS), reactive upper airway dysfunction syndrome (RUDS)

  • digestive system: nausea, diarrhoea, constipation, abdominal pain

  • immune system: frequent and prolonged infections

  • endocrine system: thyroid dysfunction

  • cardiovascular system: arrhythmias, increased heart rate, decreased blood pressure

  • musculoskeletal system: muscles and joints pain, muscle weakness, numbness

  • urogenital system: burning sensation of the mucous membrane, problem with urination

  • eyes and skin: pain, burning, itchiness, redness, discharge.

Patients experience also several general and cognitive symptoms as fatigue, chills, poor memory, thinking and concentration problems. The symptoms may be similar to those in chronic fatigue syndrome or fibromyalgia.

MCS is a real disease

MCS is not a psychosomatic illness but an overwhelmed hypersensitivity of sensory receptors together with chronic inflammation and a break-up of the body's redox system (Rea, 1996; Pall, 2007; Pall et al., 2009). Many abnormal biomarkers (‘a measurable indicator of the presence or severity of some disease state’) have been found in the peripheral circulation of patients with MCS (DeLuca et al., 2010; DeLuca et al., 2011; Belpomme et al.., 2015). Those include:

  • reduced glutathione level - a major body’s antioxidant that protects cells from damage caused by reactive oxygen species such as free radicals or heavy metals

  • reduced vitamin D2 and D3 level - a group of fat-soluble vitamins responsible for intestinal absorption of calcium, magnesium and phosphate, normal function of the immune system, heart, muscles and bones

  • elevated high sensitive C-reactive protein (hs-CRP) – a sigh of systemic inflammation

  • elevated histamine level – a marker of basophil and mast cell activation involved in the inflammatory responses

  • high level of protein S100B - a marker of blood-brain barrier dysfunction and central nervous system injury

  • elevated nitrotyrosine - an indicator or marker of cell damage, inflammation and nitric oxide (NO) production

  • increased level of heat shock proteins 27 (Hsp27) and 70 (Hsp70) – a family of proteins that are produced by cells in response to exposure to stressful conditions

  • presence of the anti-O-myelin antibodies – a biomarker of autoimmunity.

Epidemiology, risk factors and triggers

The exact world-wide incidence and prevalence of MCS are unknown. The disease occurs at all ages (also in children), regardless of gender. However, most of the patient are woman between the ages 30 and 50 years. The major risk factor is cumulative exposures to toxins, e.g., metals, volatile organic compounds (VOC) including formaldehyde, benzene, paints and solvents, as well as pesticides, tabaco smoke, diesel exhaust, cleaning products, perfumes, air fresheners and mould (Caress and Steinemann, 2004; Pall, 2009; Pigatto et al., 2013; Guzzi et al., 2016) which leads to toxicant‐induced loss of tolerance (TILT). TILT is a consequence of a two-step process (Miller, 1997):

  • step 1 – initiation and loss of tolerance in susceptible persons following exposure to various chemicals

  • step 2 – symptoms triggering by extremely small amounts of previously tolerated chemicals, drugs and foods.

Occupational exposure and indoor air are the most common source of chemical exposures. Moving to a new house or home/office renovations often bring new chemicals from furniture, paints and synthetic fabrics. Common foods may also become a trigger for people with MCS as they may contain pesticides and artificial ingredients. Various medications and medical devices also initiate and trigger MCS. Patients report that anaesthetics, implants, antibiotics, chemotherapy and other medications cause symptoms and intolerance.



· Belpomme, D., Campagnac, C. and Irigaray P. (2015). Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder. Rev Environ Health. 30:251-271.

· Caress, S. and Steinemann, A. (2004). Prevalence of multiple chemical sensitivities: a population-based study in the south eastern United States. Am J Public Health. 94:746-747.

· De Luca, C., Raskovic, D., Pacifco, V., Thai, J.C. and Korkina, L. (2011). The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances. Int J Environ Res Public Health. 8:2770-2797.

· De Luca, C., Scordo, M.G., Cesareo, E., Pastore, S., Mariani, S., Maiani, G., Stancato, A., Loreti, B., Valacchi, G., Lubrano, C., Raskovic, D., De Padova, L., Genovesi, G. and Korkina, L.G.. (2010). Biological definition of multiple chemical sensitivity from redox state and cytokine profiling and not from polymorphisms of xenobiotic metabolizing enzymes. Toxicol Appl Pharmacol. 285-292.

· Genuis, S.J. (2010). Sensitivity-related illness: the escalating pandemic of allergy, food intolerance and chemical sensitivity. Sci Total Environ. 408:6047-6061.

· Guzzi, G., Ronchi, A., Barbaro, M., Spadari, F., Bombeccari, G., Brambilla, L., Ferrucci, S. and Pigatto, P. (2016). Multiple chemical sensitivity and toxic metals. Toxicol. Lett., 258. p. s113.

· Miller C. S. (1997). Toxicant-induced loss of tolerance-an emerging theory of disease? Environmental health perspectives. 105 Suppl 2(Suppl 2), 445-453.

· Pall, M.L. (2007). Explaining ‘Unexplained Illness’: Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others. 16 Chapter book. New York: Harrington Park (Haworth) Press.

· Pall, M.L. (2009). Multiple Chemical Sensitivity: Toxicological Questions and Mechanisms, Part 8, chapter 92. Ballantyne B, Marrs TC, Syversen T, ed. General and Applied Toxicology, 3rd Ed.New Jersey: Wiley.

· Pall, M.L., Ballantyne, B., Marrs, T.C. and Syversen, T. (2009). General and applied toxicology (Chapter XX). John Wiley & Sons, Multiple Chemical Sensitivity: Toxicological Questions and Mechanisms. London.

· Pigatto, P.D., Minoia, C., Ronchi, A., Brambilla, L., Ferrucci, S.M., Spadari, F., Passoni, M., Somalvico, F., Bombeccari, G.P. and Guzzi, G. (2013). Allergological and toxicological aspects in a multiple chemical sensitivity cohort. Oxidative Med. Cell. Longev. 356235.

· Rea WJ. Chemical Sensitivity Vol. 3-Clinical Manifestation of Pollutant Overload; 1996: 1105–2015. Available at: Accessed May 5, 2018.

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