Multiple Chemical Sensitivity (MCS)

What MCS is

People with MCS report that they react to chemical levels most others tolerate, and that reactions affect multiple organ systems. Commonly used research criteria describe it as:

• a chronic condition
• with symptoms that recur reproducibly with exposure
• in response to low levels of exposure
• to multiple, chemically unrelated substances
• that improve or resolve when the triggers are removed
• affecting multiple organ systems

MCS is not recognized as a distinct disease by many medical organizations, partly because blinded studies have not shown that people with MCS can reliably detect chemicals versus placebo. However, the symptoms and disability are genuine, and patients deserve careful evaluation and support.

Symptoms

• headache or migraine-like attacks
• fatigue and exhaustion
• difficulty concentrating and memory problems
• dizziness or lightheadedness
• nausea and stomach upset
• irritation of the eyes, nose and throat
• chest tightness or breathing discomfort
• muscle and joint aches
• anxiety, irritability or low mood

Triggers

• perfumes, scented lotions and air fresheners
• laundry detergents and fabric softeners
• cleaning products and disinfectants
• tobacco smoke and vehicle exhaust
• paint, solvents, glues and new furniture or carpets (volatile organic compounds)
• pesticides
• printing ink and new plastics

Possible causes

The cause is unknown. Proposed explanations include:

• Sensitization: a large exposure, such as a chemical spill or pesticide application, may lower tolerance to later low-level exposures (the "toxicant-induced loss of tolerance" theory).
• Nervous system sensitization: heightened sensitivity of smell and pain pathways, similar to that seen in fibromyalgia and chronic fatigue syndrome, which often coexist with MCS.
• Conditioned and anxiety responses: odors linked to a previous bad experience can trigger real physical symptoms through learned responses and stress physiology.
• Unrecognized conditions: some symptoms may come from asthma, rhinitis, migraine or mast cell problems.

These mechanisms may overlap.

Conditions to rule out

Evaluation

There is no diagnostic test for MCS. A doctor will:

• take a careful history of symptoms, exposures and timing
• examine you and check breathing
• order tests to exclude other conditions, such as lung function tests, allergy testing, blood counts, thyroid function and sometimes carbon monoxide levels
• consider occupational and environmental medicine referral for workplace exposures

Unproven tests and treatments, such as hair analysis, provocation-neutralization, and chelation therapy, are not recommended and can be costly or harmful.

Management

• Reduce exposures: choose fragrance-free products, improve ventilation, use HEPA filters and activated carbon air purifiers, and avoid smoking environments.
• Workplace accommodations: fragrance-free policies, workstation relocation, ventilation changes and remote work where possible. In the US, the Americans with Disabilities Act may apply.
• Treat coexisting conditions: asthma, rhinitis, migraine, depression, anxiety and sleep disorders.
• Cognitive behavioral therapy: can reduce symptom distress and avoidance and improve function.
• Graded exposure and activity: gradually expanding the range of tolerated environments, under professional guidance.
• Self-care: regular sleep, physical activity as tolerated, stress reduction and social support.

Extreme avoidance, such as living in isolation, can increase disability and should be discussed with your care team.

Frequently asked questions

What is multiple chemical sensitivity?

Multiple chemical sensitivity is a chronic condition in which people experience symptoms such as headache, fatigue, nausea and difficulty concentrating after exposure to low levels of common chemicals, like fragrances or cleaning products, that most people tolerate.

Is multiple chemical sensitivity a real condition?

The symptoms and disability are real. However, MCS is controversial because studies have not identified a consistent biological cause or test, and many medical organizations do not recognize it as a distinct disease. Doctors focus on treating symptoms and excluding other conditions.

What triggers multiple chemical sensitivity?

Common triggers include perfumes and scented products, cleaning products, detergents, tobacco smoke, vehicle exhaust, paint, solvents, pesticides, and new building materials or furniture that release volatile organic compounds.

How is multiple chemical sensitivity treated?

There is no cure, but symptoms can be managed by reducing exposures, improving ventilation, treating related conditions such as asthma, migraine, anxiety and depression, and using cognitive behavioral therapy and graded activity to improve function and quality of life.

Is multiple chemical sensitivity an allergy?

No. MCS is not an allergy in the immune sense, and allergy tests are usually normal. However, some people have both allergies and chemical sensitivity, and true allergic reactions, such as hives or wheezing, should be evaluated separately.