What Is Chemical Sensitivity

  • Maria Conte Master's degree, Human Nutrition, Università San Raffaele, Italy
  • Ellie Kerrod BSc Neuroscience - The University of Manchester, England


We are constantly exposed to chemicals. Some are in the air, others in the products we commonly use. Some people may experience a set of symptoms from contact with these substances due to a syndrome known as Chemical Sensitivity (CS). In this article, we will explore what chemical sensitivity is, delve into its potential causes and symptoms, and discuss methods for diagnosis and potential ways to manage this condition.

What is chemical sensitivity?

Chemical sensitivity (CS), often referred to as Multiple Chemical Sensitivity (MCS), is a complex health condition that affects an undefined number of individuals. It is an acquired multifactorial syndrome characterized by a heightened sensitivity to various chemicals commonly found in our environment.1 Different terms have been used in the literature to describe this disorder, such as Chemical Intolerance (CI), Idiopathic Environmental Intolerance (IEI), and Toxicant Induced Loss of Tolerance (TILT), and they either focus on the symptoms or the mechanisms that cause the disease.2 Those with chemical sensitivity can experience a wide range of symptoms, which can be debilitating and significantly impact their quality of life. Symptoms can develop gradually over time or immediately after a single very high level chemical exposure and they involve a large spectrum of organ systems.1

The precise causes of this complex and controversial condition are not fully understood. Because of the lack of a generally accepted aetiology, diagnosis, and pathogenesis, it is also difficult to assess the prevalence.1

Causes of chemical sensitivity

As the condition is still not well defined, its existence and causes remain a topic of debate within the medical and scientific community. Volatile compounds and mixtures are considered the main triggers of the syndrome. These include substances commonly encountered in everyday life, like pesticides, cleaning products, solvents, plastics, toxic metals, car emissions, as well as some synthetic and natural fragrances, emissions from building materials, furniture, carpets, adhesives, clothing, and electrical apparatuses.1,3 Conventional toxicology can explain the effects of elevated toxic exposures, but the biological effects of low-level exposures are mostly unknown and currently under investigation.4 Several hypotheses for the causes of Chemical Sensitivity have been discussed over the years. 

Somatic or psychic?

The main debate concerns whether the disorder is of somatic or psychic origin.3

According to the somatic model, the cause would be a chemical hypersensitivity, which could be treated by avoiding exposures, while the psychosomatic model assumed a primary psychic cause.3 Psychiatrists generally assume that the syndrome is primarily a psychic disorder because patients with Chemical Sensitivity showed much higher values for somatization, compulsive disorders, depression, anxiety, and social uncertainty, as well as associations with trauma, abuse in childhood, and panic attacks.1

Main hypotheses

Toxicological, immunological, and behavioural models have been proposed over the years, but none of them has been proven.3 Most of the theories tend to break down into four main concepts involving: 

  1. Disruption in immunological/allergy processes: chemical sensitivity may result from an abnormal immune response to common chemicals, leading to heightened sensitivity and symptoms;3
  2. Alteration in nervous system function: chemicals could irritate nerve endings of sensory fibres, present in the mucous membranes of the eyes, nose, mouth, or lower airways, causing a response of the brain and the release of mediators that induce a local inflammation (neurogenic inflammation); or the limbic system, responsible for emotional and sensory processing, may become hypersensitive in individuals with chemical sensitivity, contributing to symptom development;3
  3. Changes in biochemical or biotransformation capacity: some theorists posit oxidative stress as a cause for chemical sensitivity. The presence of elevated levels of nitric oxide and peroxynitrite, two indices of oxidative stress, have been claimed to be an etiopathogenic marker in persons with this condition.1
  4. Changes in psychological/neurobehavioural function: psychological stress and trauma may play a role in the development or exacerbation of chemical sensitivity.3

There may be a genetic component to chemical sensitivity, with certain individuals having a genetic predisposition that makes them more susceptible to developing CS when exposed to chemicals. Moreover, changes in gene expression due to epigenetic factors, such as exposure to environmental toxins, could contribute to the development of the disorder.1,2

Several countries and healthcare communities have recognized chemical sensitivity or similar entities as a debilitating illness. This can only facilitate a better understanding of the factors responsible for the symptoms, regardless of their apparent etiologies.1

Symptoms of chemical sensitivity 

Chemical Sensitivity is a syndrome characterized by cutaneous, allergic, gastrointestinal, rheumatological, endocrinological, cardiological, and neurological signs and symptoms.2

Symptoms can occur after inhaling, touching, or ingesting chemical substances. 

Among the ones reported to be associated with this condition, there are increased olfactory sensitivity, dry and/or sore throat, cough, irritated or congested nose, pain in muscles and joints, difficulties concentrating, memory problems, nervousness, headache, fatigue, and skin rash.3

Diagnosing chemical sensitivity

Due to the lack of a generally accepted definition of Chemical Sensitivity, diagnostic criteria vary widely. Diagnostic procedures include a detailed case history, a physical examination, and, depending on the circumstances, laboratory investigations, organ function tests, biomonitoring, and sometimes inspection of the patient's housing conditions.1

Questionnaires like the Brief Environmental Exposure and Sensitivity Inventory (BREESI) and  the Quick Environmental Exposure and Sensitivity Inventory (QEESI©) can be used to screen patients with possible CS.2

The QEESI© was chosen to maintain international comparability and adequate accuracy.2

To better evaluate the clinical profile, patients with Chemical Sensitivity should undergo specialist evaluations, such as:

  • Allergology/Dermatologic Assessment (I Level): the syndrome has not been classified as an allergic disease, but the evidence sustains an epidemiological association with an allergic disorder;
  • Otorhinolaryngology (ORL) Assessment (I Level): to evaluate the functionality and reactivity of the upper airways together with the sensory pathway;
  • Dental Assessment (I Level): including blood/serum, urine, and saliva analyses to check toxicity from metals used in dental amalgam fillings and dental prostheses and metal crowns;
  • Neurological Assessment (I Level): environmental exposures may negatively modulate the nervous system (spatial disorientation, short-term memory loss, tinnitus, tremors, convulsions) in susceptible subjects;
  • Endocrinologic assessment (I Level): several metals as well as chemicals may interfere with the physiology of the endocrine glands, in particular, the thyroid and hypothalamic-pituitary-adrenal axis;
  • Cardiological assessment (I Level), given the wide range of comorbidities shown by patients with CS, including cardiovascular ones;
  • Rheumatologic Assessment (I Level): patients may display an association with autoimmune diseases such as Hashimoto’s thyroiditis, systemic lupus erythematosus, Sjogren’s syndrome;
  • Anesthesiologic Assessment (I Level): to especially identify and avoid anaesthetics that previously provoked anaphylaxis and/or intraoperative signs and symptoms;
  • Public Health/Occupational Medicine Assessment (I Level): recommended chemical, physical, and biological evaluations to be performed at the working site and at home to detect any recognized triggers;
  • Genetic Assessment (II Level): the MCS-related polymorphism screening remains not diagnostic but only a complementary test;
  • Metabolic Assessment (II Level), although metabolism perturbations due to or provoked by environmental exposures are currently under evaluation.2

Living with chemical sensitivity

We all became familiar with the use of medical devices (i.e., masks) during the COVID-19 pandemic, but mask choice is particularly important in patients with Chemical Sensitivity.

The pandemic has been challenging for those people because the use of all the chemicals, such as hand sanitisers and the variety of substances used to clean and sterilize environments, including shops, banks, restaurants, and hospitals, caused symptoms more often than would normally occur.6 To prevent daily flares, a kit of medical devices, including masks and air and water purifiers, is recommended for patients with Chemical Sensitivity, according to their clinical profile. All devices should have the CE marking to ensure that they meet high safety, health, and environmental protection requirements.2 Various unconventional and conventional therapies have been employed for Chemical Sensitivity.

Among unconventional methods, there are: 

  • neutralization: the treatment with the proper dose of the suspected chemical, a method not validated by academic medicine; 
  • orthomolecular therapy and other methods such as naturopathy, sauna, physical examinations, and fasting, although useful to some patients, are not at all specific for Chemical Sensitivity; 
  • elimination therapy, by using chelating agents to induce the elimination of heavy metals, method potentially accompanied by some risks, such as redistribution of the chemicals between the organs.3

Psychotherapeutic approaches have also been used, and good results have been observed, especially in the case of anxiety disorders.3


Chemical Sensitivity is a complex and not well-understood condition, causing a debilitating set of somatic and psychic symptoms following exposure to low-dose environmental chemicals. 

Various hypotheses have been discussed about the cause of this syndrome, and many in the medical community assume that the symptoms are physical manifestations of psychiatric illness rather than a primary medical illness. 

Indeed, more research is needed to clarify the pathogenic mechanisms, establish the specific chemicals responsible for the symptoms, as well as their relative potencies, and better differentiate between psychological and organic causes.   


What are the symptoms of chemical sensitivity?

Symptoms may vary among individuals. Reported symptoms include dizziness, difficulties concentrating, and headache; irritations of the eyes, nose, and throat; difficulty breathing; skin problems; muscle or joint pain.

What is an example of a chemical sensitivity?

People who are sensitive to chemicals may get symptoms (i.e. headaches), for example, from cigarette smoke or perfume. 

How do you get rid of chemical sensitivity?

There is no known unique therapy for chemical sensitivity, but avoiding exposures to chemicals, foods, drugs, and electromagnetic fields that trigger symptoms may be helpful. The use of medical devices like masks and air and water purifiers may also be beneficial. 

Is chemical sensitivity a mental illness?

There is no universally accepted definition of the disease. Some researchers believe symptoms are a physical manifestation of psychiatric illness rather than a primary medical condition, while other members of the medical community and organizations agree that multiple chemical sensitivity is an adverse physical response to certain chemicals.


  1. Zucco GM, Doty RL. Multiple chemical sensitivity. Brain Sci [Internet]. 29 December 2021 [cited 5 September 2023];12(1):46. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8773480/
  2. Damiani G, Alessandrini M, Caccamo D, Cormano A, Guzzi G, Mazzatenta A, et al. Italian expert consensus on clinical and therapeutic management of multiple chemical sensitivity (Mcs). Int J Environ Res Public Health [Internet]. 1 October 2021 [cited 5 September 2023];18(21):11294. Available at: https://europepmc.org/articles/PMC8582949
  3. Schwenk M. Multiple chemical sensitivity (Mcs) - scientific and public-health aspects. GMS Curr Top Otorhinolaryngol Head Neck Surg [Internet]. 28 December 2004 [cited 8 September 2023];3:Doc05. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3199799/
  4. Winder C. Mechanisms of multiple chemical sensitivity. Toxicology Letters [Internet]. 10 mach 2002 [cited 8 September 2023];128(1):85–97. Available at: https://www.sciencedirect.com/science/article/pii/S0378427401005367
  5. Molot J, Sears M, Anisman H. Multiple chemical sensitivity: It’s time to catch up to the science. Neuroscience & Biobehavioral Reviews [Internet]. 1 August 2023 [cited 5 September 2023];151:105227. Available at: https://www.sciencedirect.com/science/article/pii/S0149763423001963
  6. Gajebasia S, Butt S, Affleck A. Living with multiple chemical sensitivity during the COVID ‐19 pandemic: a patient’s perspective. Clin Experimental Derm [Internet]. May 2022 [cited 5 September 2023];47(5):963–4. Available at: https://academic.oup.com/ced/article/47/5/963/6693099
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Maria Conte

Master's degree, Human Nutrition, Università San Raffaele, Italy

Maria is a pharmacist with a long experience in pharmaceutical companies. Her expertise focuses in particular on drug safety and benefit-risk evaluation. She has also cultivated a strong interest in health, movement and nutrition, that led her first to a postgrad certification in "Stress. Sport and nutrition" and then to a full MSc in "Human Nutrition".
Maria has always had a passion for writing and she strongly believes that through effective communication we can improve patients’ lives and have a positive impact on the world.

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