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Multiple chemical sensitivity (MCS)


Related Terms
  • Allergen, allergic, allergic reaction, allergic response, annoyance reactions, anxiety, carbon monoxide, cigarette smoke, chemical irritants, chemical spill, chemicals, chlorine, depression, depressive disorder, formaldehyde, hypersensitive, hypersensitivity, immune hypersensitivity, indoor allergens, intoxication syndrome, irritational syndrome, limbic system, pollutants, TILT, toxic-induced loss of tolerance, toxins.

  • Multiple chemical sensitivity (MCS) describes an allergy-like reaction or sensitivity to chemicals. Patients who have MCS experience symptoms, including headache, skin rash, dizziness, and nausea, after exposure to chemicals that most healthy individuals can tolerate. Symptoms may develop after exposure to chemicals from products, such as perfumes, gasoline, smoke, or chlorine.
  • The duration of exposure and quantity of the chemical that can elicit a reaction varies among patients. MCS may occur if a patient was exposed to high levels of toxins from a chemical spill. It may also occur after long-term contact with low-levels of chemicals, which may be present in an office with poor ventilation. If chemicals from inside a building appear to be causing the symptoms, the condition is often called sick building syndrome.
  • Several organizations, including the American Academy of Allergy and Immunology, the American Medical Association, the California Medical Association, the American College of Physicians, and the International Society of Regulatory Toxicology and Pharmacology, do not recognize MCS has an established disease. This is because a clear relationship between chemical exposure and symptoms has not been established. Even though symptoms develop after exposure to chemicals, researchers have not discovered how the chemicals trigger the reaction. It has been suggested that MCS may be an allergic or toxic reaction to chemicals, but there is no evidence to support either of these claims.
  • Some researchers believe that symptoms are caused by psychological factors rather than physiological factors. It has been reported that 50% of patients with symptoms of MCS meet the criteria for having anxiety or depressive disorders. However, it remains unclear whether these psychological disorders are simply associated with MCS or whether they cause the condition. Studies are being conducted to determine the pathology of the disease.
  • Despite limited information about the disease, MCS is considered a valid condition for workmen's compensation claims, liability, tort, and regulatory actions.
  • MCS appears to be most common among patients who are 30-50 years old. According to the U.S. Environmental Protection Agency (EPA), about one-third of individuals who work inside buildings claim to be sensitive to one or more common chemicals.
  • Since little is known about MCS, specific treatments are unknown. However, symptoms generally subside once the patient avoids exposure to known chemical irritants. Patients can minimize exposure by purchasing hypoallergenic products. Patients who have sick building syndrome should talk to their colleagues and/or bosses to find ways to improve ventilation in the building.

Author information
  • This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (

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  • The cause of multiple chemical sensitivity (MCS) remains unknown. Healthcare providers disagree about whether symptoms are caused by physiological or psychological factors.
  • Some researches suggest that once airborne chemicals are inhaled, they may affect an area of the brain called the limbic system. The limbic system is involved in emotions, memory, and motivated behavior, which may make a patient more sensitive to a chemical odor. Scientific evidence to support this theory is lacking in the available literature.
  • It has also been suggested, but not scientifically proven, that patients with MCS have a damaged immune system.
  • Another theory, called toxic-induced loss of tolerance (TILT), suggests that exposure to chemicals may cause individuals to become sensitive to chemicals that they were once able to tolerate. The more the individual is exposed to the chemical, the more severe the reaction. However, research is needed to verify this claim.

  • Symptoms of multiple chemical sensitivity (MCS) vary widely among patients. Common symptoms include headache, fatigue, dizziness, nausea, irritability, intolerance to heat or cold, confusion, difficulty concentrating, earache, stuffy nose, itchy skin, sneezing, sore throat, impaired memory, difficulty breathing, changes in heart rate, chest pain, muscle pain or stiffness, gas or bloating, hives, skin rash, mood changes, and diarrhea.

  • Because little is known about the pathology of multiple chemical sensitivity (MCS), diagnostic tools are unavailable. Healthcare providers will conduct a physical examination and detailed medical history. Some patients may be asked to record when symptoms occur and how long they last. A diagnosis is typically made after the healthcare provider identifies a relationship between a patient's symptoms and exposure to chemicals.

  • Since little is known about MCS, specific treatments are unknown. However, symptoms generally subside once the patient discontinues exposure to known chemical irritants.
  • Proper ventilation can help decrease the number of chemicals and irritants in the air.
  • Keep the windows closed when driving, especially in areas of high traffic. Many chemicals in gasoline and diesel can trigger a reaction in patients who have MCS.

Integrative therapies
  • Note: Currently, there is insufficient available evidence on the safety and efficacy of integrative therapies for the treatment or prevention of multiple chemical sensitivity (MCS). The therapies listed below have been studied for related conditions such as allergies and chemical toxicity, should be used only under the supervision of a qualified healthcare provider, and should not be used in replacement of other proven therapies or preventive measures.
  • Good scientific evidence:
  • Chelation: EDTA chelation became well known during the 1950s, when it was proposed as a method to cleanse the blood and blood vessel walls of toxins and minerals. For many years, chelation therapy has been used with calcium disodium EDTA to treat heavy metal toxicity. It is still an accepted medical therapy for lead toxicity, and several studies report lower levels of lead in the blood and slower progression of kidney failure. Chelation therapy may also be used to treat iron, arsenic, mercury, or cobalt poisoning. However, some research results are mixed. More studies are needed to clarify.
  • Avoid in patients taking anticoagulants or antiplatelets. Avoid during root canal therapy. Avoid if pregnant or breastfeeding.
  • Unclear or conflicting scientific evidence:
  • Applied kinesiology: Applied kinesiology is commonly used for food allergy diagnosis. However, there is conflicting scientific evidence as to whether applied kinesiology is an effective diagnostic tool. Further research is warranted before a firm conclusion can be drawn.
  • Applied kinesiology techniques in themselves are generally considered to be safe. However, medical conditions should not be treated with AK alone, and should not delay appropriate medical treatment.
  • Black seed: Studies in patients with allergies found that black seed decreased allergic disease severity. The effect of black seed for allergies is still not clear and further study is required.
  • Avoid with a known allergy/hypersensitivity to black seed, its constituents, black seed oil, or to members of the Ranunculaceae family. Allergic contact dermatitis has been reported after topical use of black seed or the oil from the seed.
  • Calcium: A chelating treatment of calcium has been suggested to reduce blood levels of lead in cases of lead toxicity. Reduced symptoms have been observed in most, but not all, patient case reports and case histories. Adequate calcium intake appears to be protective against lead toxicity. Treatment of lead toxicity should only be done under supervision of a qualified healthcare professional.
  • Avoid if allergic or hypersensitive to calcium or lactose. High doses taken by mouth may cause kidney stones. Avoid with high levels of calcium in the blood, high levels of calcium in urine, high levels of parathyroid hormone, bone tumors, digitalis toxicity, ventricular fibrillation, kidney stones, kidney disease, or sarcoidosis (inflammation of lymph nodes and various other tissues). Calcium supplements made from dolomite, oyster shells, or bone meal may contain unacceptable levels of lead. Use cautiously with achlorhydria (absence of hydrochloric acid in gastric juices) or irregular heartbeat. Calcium appears to be safe during pregnant or breastfeeding women; talk to a healthcare provider to determine appropriate dosing during pregnancy and breastfeeding.
  • Cat's claw: It has been suggested that cat's claw may help treat allergies. However, there is limited scientific evidence to support this claim. More well-designed trials are needed to determine whether cat's claw is a beneficial treatment.
  • Avoid if allergic to cat's claw or Uncaria plants or plants in the Rubiaceae family such as gardenia, coffee, or quinine. Avoid with a history of conditions affecting the immune system (such as AIDS, HIV, some types of cancer, multiple sclerosis, tuberculosis, rheumatoid arthritis, lupus). Use cautiously with bleeding disorders or a history of stroke, or if taking drugs that may increase the risk of bleeding. Discontinue use two weeks before surgery/dental/diagnostic procedures with bleeding risk, and do not use immediately after these procedures. Cat's claw may be contaminated with other Uncaria species. Reports exist of a potentially toxic, Texan grown plant, Acacia gregii being substituted for cat's claw. Avoid if pregnant, breastfeeding, or trying to become pregnant.
  • Chlorophyll: Chlorophyll is a chemoprotein commonly known for its contribution to the green pigmentation in plants, and is related to protoheme, the red pigment of blood. It can be obtained from green leafy vegetables (broccoli, Brussels sprouts, cabbage, lettuce, and spinach), algae (Chlorella and Spirulina), wheat grass, and numerous herbs (alfalfa, damiana, nettle, and parsley). Yusho poisoning is caused by ingestion of rice oil contaminated with polychlorinated biphenyls, specifically polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs). A chlorophyll-rich diet may increase PCDF and PCB elimination, but further high quality research is needed.
  • Avoid if allergic or hypersensitive to chlorophyll or any of its metabolites. Use cautiously with photosensitivity, compromised liver function, diabetes, or gastrointestinal conditions or obstructions. Use cautiously if taking immunosuppressants or antidiabetes agents. Avoid if pregnant or breastfeeding.
  • Clay: Clay lozenges have been used historically in the treatment of mercuric chloride poisoning and were officially mentioned in several European pharmacopoeias, including the Royal College, until the middle 19th Century. However, there is not enough scientific evidence to recommend the use of clay by mouth for mercuric chloride poisoning at this time, as there is a risk of clay itself containing contaminants.
  • There is a lack of reports of allergy to clay in the available scientific literature. However, in theory, allergy/hypersensitivity to clay, clay products, or constituents of clay may occur. Avoid if pregnant or breastfeeding.
  • Folate (folic acid): Folate and folic acid are forms of a water-soluble B vitamin. Folate occurs naturally in food, and folic acid is the synthetic form of this vitamin. Folate may lower blood arsenic concentrations and thereby contribute to the prevention of arsenic poisoning. Additional research is needed in this area.
  • Avoid if allergic or hypersensitive to folate or any folate product ingredients. Use cautiously if receiving coronary stents or with anemia or seizure disorders. It is recommended that pregnant women consume 400 micrograms of folate daily in order to reduce the risk of fetal defects. Folate is likely safe if breastfeeding.
  • Hypnotherapy, hypnosis: It has been suggested that hypnotherapy may be effective for allergies. However, further research is necessary to determine whether it is an effective treatment.
  • Use cautiously with mental illnesses like psychosis/schizophrenia, manic depression, multiple personality disorder or dissociative disorders. Use cautiously with seizure disorders.
  • Iron: Iron deficiency may increase the risk of lead poisoning in children. However, the use of iron supplementation in lead poisoning should be reserved for those individuals who are truly iron deficient or for those individuals with continuing lead exposure, such as continued residence in lead-exposed housing.
  • Iron is a trace mineral, and hypersensitivity is unlikely. Avoid with known allergy/hypersensitivity to products containing iron. Avoid excessive intake. Avoid iron supplements with blood disorders that require frequent blood transfusions. Use iron supplements cautiously with a history of kidney disease, intestinal disease, peptic ulcer disease, enteritis, colitis, pancreatitis, hepatitis, alcoholism, or with a history of heart disease. Use cautiously in those who plan to become pregnant, or in those older than age 55. Pregnant or breastfeeding women should consult their healthcare professionals before beginning iron supplementation.
  • Lactobacillus acidophilus: Limited available study suggests that the Lactobacillus acidophilus (L. acidophilus) strain L-92 (L-92) may be effective for the treatment of Japanese cedar-pollen allergy. Further research is needed to confirm these results.
  • L. acidophilus may be difficult to tolerate if allergic to dairy products containing L. acidophilus. Avoid with history of an injury or illness of the intestinal wall, immune-disease, or heart valve surgery. Avoid with prescription drugs, such as corticosteroids, because of the risk of infection. Use cautiously with heart murmurs. Antibiotics or alcohol may destroy L. acidophilus. Therefore, it is recommended that L. acidophilus be taken three hours after taking antibiotics or drinking alcohol. Some individuals may use antacids, such as famotidine (Pepcid®) and esomeprazole (Nexium®), to decrease the amount of acid in the stomach one hour before taking L. acidophilus.
  • Onion: Research shows that topical application of an alcoholic onion extract significantly reduced responses to allergies. Although intriguing, more research is needed in this area to establish the efficacy and dosing of topical onion extracts.
  • Avoid if allergic or hypersensitive to onion (Allium cepa), its constituents, or members of the Lilaceae family. Use cautiously with hematologic (blood) disorders, diabetes, hypoglycemia (low blood sugar), and hypotension (low blood pressure). Use cautiously if taking anticoagulants or antiplatelets (blood thinners). Avoid medicinal doses if pregnant or breastfeeding.
  • Perilla: Preliminary evidence suggests some benefit of perilla extract for allergies. Further clinical trials are required before conclusions can be made.
  • Avoid if allergic/hypersensitive to perilla or members of the Lamiaciae/Labiatae family. Use cautiously with cancer, low HDL-cholesterol, and immune disorders. Use cautiously if taking NSAIDS or barbiturates. Avoid if pregnant or breastfeeding.
  • Probiotics: Only a few types and combinations of probiotics have been studied as a possible allergy treatment. They have been studied mostly in children, teenagers, and young adults. Further research is necessary before a firm conclusion can be made.
  • Probiotics are generally considered safe and well tolerated. Avoid if allergic or hypersensitive to probiotics. Use cautiously if lactose intolerant.
  • Reishi: Reishi mushroom (Ganoderma lucidum), also known as ling zhi in China, grows wild on decaying logs and tree stumps. Reishi occurs in six different colors, but the red variety is most commonly used and commercially cultivated in East Asia and North America. Ganoderma lucidum has shown a beneficial effect in treating Russula subnigricans (RSP) poisoning in limited study. Further well-designed clinical trials are needed to confirm these results.
  • Avoid if allergic or hypersensitive to any constituents of Ganoderma lucidum or any member of its family. Use cautiously with diabetes, blood disorders (including hemophilia), low blood pressure, or ulcers. Reishi is likely safe when consumed in amounts generally found in foods in non-allergic pregnant or breastfeeding women.
  • Safflower: Based on preliminary study, safflower (Carthamus tinctorius) oil may effectively remit the symptoms of neurotoxicity from lithium. However, more studies are needed to better understand safflower's effect on lithium toxicity.
  • Avoid if allergic/hypersensitive to safflower, safflower oil, daisies, ragweed, chrysanthemums, marigolds, or any related constituents. Use parenteral safflower oil emulsions cautiously in newborns. Use cautiously if taking anticoagulants (blood thinners) or anti-platelet drugs, immunodepressants or pentobarbital. Use cautiously with diabetes, low blood pressure, liver problems, bleeding disorders, or skin pigmentation conditions. Use cautiously if pregnant or breastfeeding.
  • Spirulina: The term spirulina refers to a large number of cyanobacteria or blue-green algae. Spirulina extract plus zinc may be useful for the treatment of arsenic poisoning. Additional research is needed to confirm early study findings.
  • Avoid if allergic or hypersensitive to spirulina or blue-green algae. Use cautiously with phenylketonuria, autoimmune diseases, bleeding disorders, diabetes, osteoporosis or if taking products containing the blue-green algae species Anabaena spp., Aphanizomenon spp., and Microcystis spp. Use cautiously in underweight patients or in those taking antiobesity agents or appetite suppressants. Use cautiously if consuming a high-protein diet. Avoid in children and pregnant or breastfeeding women.
  • Thymus extract: Thymus extract may reduce allergy symptoms due to its potential immune stimulating effects. More clinical trials are required before recommendations can be made involving thymus extract for this use.
  • Avoid if allergic or hypersensitive to thymus extracts. Use bovine thymus extract supplements cautiously due to potential for exposure to the virus that causes "mad cow disease." Avoid use with an organ transplant or other forms of allografts or xenografts. Avoid if receiving immunosuppressive therapy, with thymic tumors, myasthenia gravis (neuromuscular disorder), untreated hypothyroidism, or if taking hormonal therapy. Avoid if pregnant or breastfeeding; thymic extract increases human sperm motility and progression.
  • Zinc: Limited available study has shown that a combination of spirulina extract plus zinc may be useful for the treatment of chronic arsenic poisoning with melanosis and keratosis. More research is needed to confirm the effects of zinc alone.
  • Zinc is generally considered safe when taken at the recommended dosages. Avoid zinc chloride because evidence of safety and effectiveness are currently lacking. Avoid with kidney disease. Use cautiously if pregnant or breastfeeding.
  • Selenium: Selenium is a mineral found in soil, water, and some foods. Selenium has been proposed as a potential treatment for arsenic poisoning, although reliable evidence is currently lacking in this area.
  • Avoid if allergic or sensitive to products containing selenium. Avoid with a history of non-melanoma skin cancer. Selenium is generally regarded as safe for pregnant or breastfeeding women. However, animal research reports that large doses of selenium may lead to birth defects.

  • Avoid or minimize exposure to known chemical irritants. Patients can purchase hypoallergenic products. If food additives, preservatives, or artificial sweeteners are suspected triggers, patients can purchase organic or "all natural" foods.
  • Proper ventilation can help decrease the number of chemicals and irritants in the air. Consider installing central air conditioning with a high-efficiency particulate air (HEPA) filter attachment. These air filters can remove many airborne pollutants that may trigger a reaction.
  • Keep the windows closed when driving, especially in areas of high traffic. Many chemicals in gasoline and diesel can trigger a reaction in patients who have multiple chemical sensitivity (MCS).

Common triggers
  • General: Multiple chemical sensitivity (MCS) may occur after exposed to high levels of toxins from a chemical spill. It may also occur after long-term contact with low-levels of chemicals that may be present in an office with poor ventilation. If chemicals from inside a building appear to be causing the symptoms, the condition is often called sick building syndrome. Areas of poor ventilation increase the number of chemicals and irritants in the air.
  • Buildings: Sick building syndrome occurs most often in new buildings that are designed to be energy-efficient, have windows that do not open, and have poor ventilation. These buildings often have high levels of carbon dioxide, which is a frequent cause of sick building syndrome. Chemicals found in renovation supplies, cleaning agents, and office machinery may also cause the reaction.
  • Cigarette smoke: Cigarette smoke is one of the most common causes of MCS. The smoke from cigarettes contains many chemicals, irritants, and gases, including formaldehyde, nacrolein, polycyclic aromatic hydrocarbons, hydrogen cyanide, carbon monoxide, nitrogen dioxide, and acrolein. Exposure to smoke indoors or in areas of poor ventilation significantly increases the amount of chemicals and toxins in the air.
  • Formaldehyde: Formaldehyde, which is also present in cigarette smoke, is present in gasoline and diesel combustion as well. Individuals are often exposed to these chemicals when they are waiting in traffic, especially if the windows are rolled down.
  • Wood-burning stoves: A gas called carbon monoxide is released into the air when wood is burned. When wood is burned during cold temperatures (e.g. fireplaces during the winter months), the amount of carbon monoxide released into the air increases. Also, poorly ventilated stoves release carbon monoxide, nitrogen, sulfur oxides, formaldehyde, and benzopyrene. All of these chemicals can potentially trigger a reaction in MCS patients.
  • Other: Other common triggers include perfume, nail polish remover, newspaper ink, hairspray, paint or paint thinner, insecticides, artificial colors, artificial sweeteners, food preservatives, adhesive tape, new carpets, flame retardants on clothing and furniture (such as mattresses), felt tip pens, chlorine in swimming pools, as well as chemicals from dust, pollens, animal dander, and molds.

Other types of chemical sensitivities
  • Annoyance reactions: Annoyance reactions occur when the patient is overly sensitive to unpleasant odors. Some patients are born with this sensitivity, while others become sensitive after they develop an infection, abuse tobacco, overuse nasal decongestants, or after the lining of the nose becomes inflamed.
  • Immune hypersensitivity (allergic reaction): An immune hypersensitivity is an allergic reaction to chemicals. This occurs when the body's immune system overreacts to chemicals that enter the body. The white blood cells launch an attack against chemicals because they are mistaken for harmful invaders, such as bacteria or viruses. This reaction causes allergy symptoms, such as hives, skin rash, and headache, to develop. Allergic reactions usually occur in response to chemicals that are found in pollens, dust mites, and molds. Only a few industrial chemicals, which are used to produce consumer goods, have been shown to cause an allergic reaction. Examples include acid anhydrides and isocyanates.
  • Intoxication syndrome: Intoxication syndrome is the most severe type of reaction to chemicals. This typically occurs after long-term exposure to harmful chemicals, which may be present in pesticides, cleaning fluids, or paints. Intoxication syndrome is not an allergic reaction because it does not involve the immune system. Intoxication syndrome may cause a serious illness, which may lead to death in some patients.
  • Irritational syndromes: Irritational syndromes may occur after a patient is exposed to significant amounts of irritating chemicals. These chemicals may affect nerves in the body involved with physical sensations. As a result, patients with irritational syndromes often experience burning sensations in the nose, eyes, and throat after exposure to certain chemicals. Symptoms usually come and go, and they do not cause permanent damage.

Copyright © 2011 Natural Standard (

The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.

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