Multiple Chemical Sensitivity

About Multiple Chemical Sensitivity

Multiple Chemical Sensitivity (MCS) is a condition experienced by many people with fibromyalgia and chronic fatigue syndrome. Some people with Post Traumatic Stress Disorder (PTSD) also report chemical sensitivities, as do many people with Gulf War Syndrome (GWS).

Many researchers now believe that these multi-system illnesses are all part of a family of illnesses known as “functional somatic syndromes” which in recent times have been referred to as Central Sensitivity Syndromes.

In central sensitivity syndromes, the nervous system becomes inflamed and hyper-responsive to certain stimuli. Those stimuli can include pain, temperature, light, noise and, especially in the case of MCS, chemicals and scents. This may or may not also be connected to Mast Cell Activation Disease (MCAD), which is a disorder that can also result in multi-system symptoms and sensitivity to chemicals. People with MCS and/or MCAD are thought to experience quite severe disturbances to the HPA axis and functioning of the Autonomic Nervous System (dsyautonomia)

The World Health Organisation (WHO) classifies Multiple Chemical Sensitivity (MCS) as an idiopathic environmental intolerance (IEI) (1996) along with electro-sensitivity (2004). A small percentage of people with MCS also experience electro-sensitivity.

Multiple Chemical Sensitivity is still a controversial diagnosis. Many health practitioners without training in ecology or environmental medicine or without specialised knowledge in chronic fatigue and fibromyalgia related illness believe MCS is a psychological or psychiatric illness. While many people with MCS do indeed experience co-morbid psychiatric illnesses like major depression disorder (MDD), recent research indicates that MCS has a pathophysiological basis and psychological illness is usually secondary. Often caused by the additional bio-psycho-social stresses experienced as a consequence of living with a painful chronic illness.

While some people with less severe MCS, do benefit from psychological and psychiatric interventions, the vast majority of people with MCS report these interventions worsen symptoms. While nobody is exactly sure of the reason for this, it has been linked to poor tolerance to psychogenic medications due to liver detoxification impairment (FLDP Test not standard liver test), nerve inflammation, and most likely pharmacological food intolerance. Poor tolerance to psychological interventions like Cognitive Behavioral Therapy (CBT) is common to people experiencing hypocortisolism. Which is generally a consequence of neural sensitisation (changes to the nervous system and brain that makes these more sensitive to stressors) causing over activation of the stress response and limbic HPA axis dysregulation.


diagram source: chronic multi-system illness University Michigan Health

Symptoms reported by people with MCS can be just about anything. The most common symptoms are the same as those experienced by people with to fibromyalgia (FMS) and chronic fatigue syndrome (CFS). They include:

  • Sleep difficulties
  • Memory and Concentration difficulties
  • Headaches/migraines
  • Dizziness
  • Severe fatigue
  • Muscle and joint pain
  • Digestive upsets
  • Mood disturbances

Other symptoms more specific to people with chemical sensitivities include:-

  • Stinging eyes
  • Wheezing and breathlessness
  • Runny nose and sinus problems
  • Rashes
  • More severe agitation and emotional distress


Many symptoms experienced by people with MCS are triggered or worsened by exposures to scents and products high in Volatile Organic Compounds (VOCS). For example many

  1. Cleaning and laundry products
  2. Personal Care and Beauty Products
  3. Building materials e.g. paint, composite woods, solvent based glues
  4. Home furnishings
  5. Electronics
  6. Gas Appliances
  7. Art Supplies

Certain medications, supplements and food stuff are also likely to trigger and worsen symptoms in people with MCS.

These unpleasant reactions to substances normally tolerated by most people is thought to be a consequence of a very high total stress load (load phenomena) and lowered threshold limits (tolerance) to stressors because of a poor relaxation response, cortisol depletion, impaired detoxification and lifestyle and dietary factors. Poor sleep and continued exposures to environmental toxins (mold and chemicals), as well as hormone fluctuations, lack of exercise and illness can further reduce tolerance and increase sensitivities.

Symptom relief

Significant "sustainable" symptom relief can usually be achieved by calming the stress response, mast cell activation and addressing HPA axis dysregulation. This generally requires a multi-dimensional treatment approach that starts with targeting the most problematic symptoms first.


Nobody knows the exact cause of multiple chemical sensitivity, however there are many proposed theories that are now becoming scientifically validated

The two dominant theories are Dr Martin Pall's NO/OONO disease cycle and the bucket (or barrel) theory (also known as load phenomena and total stress load). The bucket theory simply implies that a person toxicity, inflammation and stress load is too high, because exposures to everyday stressors including chemicals, stimuli, scents, food stuff and psychological and social stressors exceed their capacity and because of this they get unpleasant symptoms. Everybodies bucket size is different and is influenced by genetics.

Dr Martin Pall says that the NO/OONO disease cycle is initiated by a heightened stressor (physical, psychological, chemical injury, infection) in people with a vulnerable genetic profile or people who have experienced a very extreme stressor i.e.Trauma.

Another theory called Toxicant Induced Loss of Tolerance (TILT) is proposed by Dr Claudia Miller.

    “MCS appears to evolve in two stages: (1) initiation, characterized by a profound breakdown in prior, natural tolerance resulting from either acute or chronic exposure to chemicals (pesticides, solvents, indoor air contaminants, etc.), followed by (2) triggering of symptoms by small quantities of previously tolerated chemicals (traffic exhaust, fragrances, gasoline), foods, drugs, and food/drug combinations (alcohol, caffeine).” (Miller -2)

Dr Jay Seastrunk says that the main maintainer of Multiple Chemical Sensitivity is Limbic Kindling and Neural Sensitisation - this is supported by Dr Martin Palls postulated NO/OONO disease cycle which indicates that complex multi-system illness (also known as central sensitivity syndromes) are chronic neuro inflammatory conditions which lead to multi-system symptom that are non specific in nature, along with heightened pain and heightened sensitivity.


[1] Bell I.R., Schwartz G.E., Baldwin C.M., Hardin E.E., Neural Sensitization and Physiological Markers in Multiple Chemical Sensitivity, Regulatory Toxicology and Pharmacology, 24: S39 – S47 (1996)

[2] Miller C.S., The Compelling Anomaly of Chemical Intolerance, Annals of the New York Academy of Sciences, 933 (1): 1-23 (2001)

[3] Sorg B.A., Multiple Chemical Sensitivity: Potential Role for Neural Sensitization, Critical Reviews in Neurobiology 13 (3) (1999)

[4] Seastrunk J. KINDLING , FOCAL BRAIN INJURY AND CHEMICAL and ELECTRICAL SENSITIVITY in the production of “Environmental Disease”

[5] Pall M.L.(2007) Explaining “Unexplained Illnesses”: Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromylagia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others. Harrington Park (Haworth) Press, New York.

[6] Yunus M Fibromyalgia and Overlapping Disorders: The Unifying Concept of Central Sensitivity Syndromes

[7] Bell I.R., White Paper: Neuropsychiatric aspects of sensitivity to low-level chemicals: a neural sensitization model, Toxicology and Industrial Health, 10 (4/5): 277 - 312 (1994)

[8] Hooper M Engaging with Multiple Chemical Sensitivity (MCS)- London (2003) Malcolm Hooper PhD, B Pharm, C Chem, MRIC Chief Scientific Advisor to the Gulf War Veterans

[9] What Causes Multiple Chemical Sensitivity – MCS Research from James Madison University

[10] Heuser, G., Mena, I., Alamous, F. "Neurospect Findings in Patients Exposed to Neurotoxic Chemicals." Toxicology and Industrial Health 10, nos. 4-5 (1994):461-571.

[11] Heuser, G., Mena, I. "Neurospect in Neurotoxic Chemical Exposure. Demonstration of Long-Term Functional Abnormalities." Toxicology and Industrial Health 14, no. 6 (1998):813-827.

[12] Dr Sarah Myhill Chemical Poisoing – general principles of diagnosis and treatment

[13] The Search for Reliable Biomarkers of Disease in Multiple Chemical Sensitivity and Other Environmental Intolerances Chiara De Luca,1,* Desanka Raskovic,1 Valeria Pacifico,1 Jeffrey Chung Sheun Thai,2 and Liudmila Korkina1.

[14] Donohue M. Report # 4 Neural Sensitisation - Toxipedia

[15] Limbic system mechanisms of stress regulation: Hypothalamo-pituitary-adrenocortical axis James P. Herman a,b,*, Michelle M. Ostrander a, Nancy K. Mueller a, Helmer Figueiredo a

For full bibliography click here