L'Association pour la santé environnementale du Québec / Environmental Health Association of Québec

Diagnosis, Treatment, Resources

What are Environmental Sensitivities/Multiple Chemical Sensitivities (MCS)

Environmental sensitivities/multiple chemical sensitivities (MCS) are a range of reactions to environmental factors, including chemicals, foods, and biological agents at levels of exposure tolerated by many people.

MCS is a painful, chronic, multi-system condition that can develop in people of all ages, often following either a single massive exposure or repeated low-level exposures to commonly used products, and chemicals commonly released into the environment.

Sufferers then become sensitized to substances in their everyday environment at levels well below what would be considered to be acceptable to “normal” people. Sensitivity reactions can be triggered by scented products (personal products, shampoo, antiperspirants, creams, cologne, clothes softener, etc.), cleaning products, laundry detergents, paints, petrochemicals, cigarette smoke, pesticides, pets, plants, solvents, molds, foods or additives, etc.

Examples of triggers / exposures (Non exhaustive list)

Click here to view more triggers

Chemical agentsFlame retardants, rubber, volatile organic compounds (VOCs), diesel, ink and printed material, petrol or natural gas, smoke (tobacco, wood, etc.), vehicle exhaust, fresh tar or asphalt, interiors of new cars, dry cleaning fluid, building and renovation materials (e.g. caulking, grout, shellac, paint, sealants, varnish, etc.), markers, new furniture and furnishings, new carpets, pesticides, petrochemicals, insecticide spray, shower curtains, chemicals and VOCs released by new products, nail polish and solvents, soft vinyl, etc.
Biological agentsMould
Glues and solvents, exposures to volatile organic compounds (VOCs), exposures to gases and fumes (firefighters), gases and fumes from welding, exhaust gases, Isocyanates, paints and paint thinners, pesticides, dust from wood, flour, metal, etc., chemicals used in the manufacture of plastics, adhesives, etc.
Scented productsAir fresheners and incense, fabric softeners, sunscreen, detergents and soaps, new plastic, cleaning products (e.g. disinfectants, bleach, floor cleaners, furniture cleaners, etc.), personal care products (e.g. : deodorants, hair spray, body lotions, aftershave lotions, makeup, etc.), baby care products, perfumed products (colognes, essential oils, perfumes, devices emitting all kinds of perfumes, potpourris), etc.
OtherFoods, supplements, medications, food flavourings, colours, preservatives, etc., sound, vibration, light, temperature, wood terpenes, etc.

This is not an exhaustive list of exposures in the workplace. Sensitivities caused by a substance
can lead to reactions to other chemicals, including unrelated personal and household cleaning
products, smoke, food, etc.

Symptoms (Non-exhaustive list)

Click here to view symptoms

Central Nervous &
Sense of smell heightened, neurological pain (skin burning most often), migraines, intense headaches, dizziness, vertigo, confusion, feeling dull, weak or foggy, lack of coordination and / or balance, tinnitus, cognitive problems (brain fog), poor concentration, difficulty remembering, memory loss, hyperactivity, restlessness, anxiety, tension, depression, insomnia, sleep problems, night sweats, fatigue, exhaustion
Respiratory & ImmuneDistress and / or difficulty breathing, coughing, wheezing, shortness of breath, asthma, chest pain, frequent bronchitis or pneumonia, congestion, itching or runny nose, allergic rhinitis, sinus infections and / or pain, sore throat, swollen glands, flu-like symptoms
EyesRed, painful, watery eyes, disturbed vision
GastrointestinalExcessive drooling, bleeding gums, heartburn, abdominal or stomach pain, nausea, bloating, constipation, diarrhea
EndocrineFatigue, lethargy, fluctuating blood sugar, hormonal disturbances or imbalances
Musculo skeletalMuscle spasms and / or pain, joint pain and / or swelling, backache, burning sensation in the muscles, extreme pain in the face, jaws and mouth, weakness, allodynia, inflammation
CardiovascularPalpitations, rapid and / or irregular heartbeat, hypertension or hypotension, cold extremities
SkinEczema, rashes, itching, hives, redness, rash, redness, cuts or lesions
GenitourinaryFrequency and urgency to urinate, incontinence, spasms in the bladder

Diagnostic Criteria

Taking an Exposure History (CH2OPD2)
The Quick Environmental Exposure and Sensitivity Inventory (QEESI)

Multiple Chemical Sensitivities (MCS)

Initiation and subsequent sensitization observed in cases of environmental sensitivities:

  1. Symptoms are reproducible following repeated chemical exposure;
  2. The condition is chronic;
  3. Lower exposure levels than those previously tolerated, or tolerated by the general population, lead to the manifestation of symptoms;
  4. Symptoms improve or disappear when the incitants are removed;
  5. Responses occur to multiple chemically unrelated substances;
  6. Symptoms involve multiple organ systems;
  • Still not refuted in the literature published almost two decades later
  • Definition used both in clinical practice and in research
  • Recently (2018) confirmed by the MOHLTC of Ontario by a group of experts using the Delphi process

Bartha, L., et al., Multiple chemical sensitivity: a 1999 consensus. Archives of Environmental Health: An International Journal, 1999. 54(3): p. 147-149.
McKeown-Eyssen, G.E., et al., Multiple chemical sensitivity: discriminant validity of case definitions. Archives of Environmental Health: An International Journal, 2001. 56(5): p. 406-412.
Nethercott, J.R., et al., Multiple chemical sensitivities syndrome: toward a working case definition. Archives of Environmental Health: An International Journal, 1993. 48(1): p. 19-26.
Ontario Ministry of Health and Long-Term Care, Guiding Principles for the Diagnosis of Environmental Sensitivities/Multiple Chemical Sensitivity. Centre for Effective Practice, 2018.


Ottawa Environmental Health Clinic:

The basic principle of treatment is the avoidance of triggers, so as to create an environment where the body can heal:

  • Recognize the current or potential triggers, by taking the exposure history of the person: community, housing, hobby (leisure), occupation, personal, diet, drugs (drugs) (CH2OPD2);
  • Consider current or potential exposures as well as stresses that may contribute to the condition, reducing or eliminating them as much as possible;
  • Identify the toxic load of the body, such as heavy metals or chlorine compounds, using appropriate tests, and intervene in a targeted manner to reduce this overload.
  • Make up for nutritional deficiencies such as vitamins and minerals, which make it more difficult for the person to metabolize the triggering agents;
  • Opt for organic food.

Support for people who suffer from Multiple Chemical Sensitivities (MCS)

A diagnosis is necessary as the first means of support.

Environmental health in hospitals – A practical guide for hospital employees:

Part 1 : Pollution Prevention
Part 2 : Environment-Sensitive Care

Maintain employment and / or avoid isolation, stigma and exclusion:

Letters of support for accommodation in the workplace (e.g. fragrance-free environment, ecological renovations, cable Internet connection rather than Wi-Fi, good ventilation, avoidance of triggers (for example, avoid isocyanates by substitution), etc.).

To help the person manage their sensitivities as well as possible and keep their job, a letter explaining their needs is useful.

Tips for obtaining accommodation without a lawyer

For more information on personal accommodation, please visit:

In order to implement a fragrance-free policy in your health-care establishment:

List of products generally tolerated

(Using less toxic products is a way to prevent environmental sensitivities/multiple chemical sensitivities)

How to choose healthy products – for persons who suffer from environmental sensitivities and for their entourage

Ecological solutions for everyday living

Information on mould