Clinical Assessment
How Is MCS Diagnosed?
Diagnosis of Multiple Chemical Sensitivity (MCS) is based on clinical assessment. A thorough evaluation includes medical and exposure history, physical examination, and appropriate investigations to rule out other conditions.
Six Internationally Recognized Diagnostic Criteria — 1999 Consensus Statement
Reproducible Symptoms
Symptoms are reproducible with repeated chemical exposure
Chronic Condition
The condition is chronic, not episodic or temporary
Low Exposure Threshold
Reactions occur at low levels of chemical exposure
Improves on Avoidance
Symptoms improve or resolve when exposure is removed
Multiple Substances
Multiple unrelated chemical substances cause reactions
Multi-System Impact
Multiple body systems are affected by reactions
Diagnosis is based on clinical assessment, medical and exposure history, and systematic investigation.
Validated Assessment
Validated Screening Tools
Two validated screening tools support clinical assessment and case identification of Multiple Chemical Sensitivity (MCS). They help clinicians and patients identify patterns of chemical sensitivity and document exposure history.
BREESI
The Brief Environmental Exposure and Sensitivity Inventory (BREESI) is a short, validated screening questionnaire to identify individuals who may have MCS or chemical intolerance. Typically used before the QEESI.
Download BREESI (PDF)
QEESI
The Quick Environmental Exposure and Sensitivity Inventory (QEESI) is a validated comprehensive assessment tool evaluating severity and patterns of chemical sensitivity — covering exposure history, symptom burden, and impact on daily life.
Access QEESI (ECRoB Version)Activity and Symptom Tracking
Tracking symptoms over time helps build the exposure history needed for accurate clinical assessment. The following tools are available for patients and clinicians.
Challenges & Context
Why Diagnosis Can Be Difficult
Despite internationally recognized criteria, many people living with Multiple Chemical Sensitivity (MCS) experience significant delays in receiving a diagnosis. Without documentation, accessing accommodations, disability supports, and appropriate care becomes much harder.
Common Barriers to Diagnosis
An environmental health clinic in Toronto provides diagnostic services and clinical support. Comparable services remain limited across much of Canada. If you are seeking a diagnosis, asking your primary care provider for a referral to an environmental medicine specialist is a reasonable starting point.
"The only reason my MD believes me is because I had an outright reaction right in front of him."
— Focus group participant, ASEQ-EHAQ, Accessible Air in the Built Environment, 2024
There is currently no cure for MCS. The most effective approach is ongoing management through consistent, systematic reduction of exposures to known and potential triggers.
Management & Care
Current Treatment Approaches
The medical literature indicates that the most effective approach is ongoing management through consistent, systematic reduction of exposures to known and potential triggers.
The TILT Framework
The Toxicant-Induced Loss of Tolerance (TILT) framework is a clinically recognized model for understanding chemical intolerance and MCS. It describes a two-stage process: initial loss of tolerance following significant exposure, followed by ongoing triggering at lower levels.
Initiation
Significant or repeated chemical exposure leads to initial loss of tolerance — the body's response threshold changes permanently
Triggering
Ongoing symptoms triggered by lower-level exposures to chemicals across multiple, unrelated substance classes
Evidence-Based Management Principles
Identify and reduce exposure to known triggers, beginning with the highest-exposure environments
Prioritize fragrance-free, lowest VOC emission, and least-toxic product choices
Improve indoor air quality in the home, workplace, school, and healthcare settings
Establish routines that protect energy, support stability, and reduce cumulative exposure
Work with a healthcare provider to document functional limitations and required accommodations
Consider supervised trials of avoidance to identify which exposures are most problematic
Management is not passive. It requires active, ongoing attention to environments, products, and habits. Early and consistent exposure reduction generally leads to better functional outcomes.
Treatment Resources
Downloads & References
Key Resources
Clinical tools and research references for patients, caregivers, and healthcare providers navigating diagnosis and care for Multiple Chemical Sensitivity (MCS).
Taking an Exposure History
Clinical tool for documenting patient exposure history. Useful for both patients and providers during the diagnostic process.
Download PDF
BREESI Screening Questionnaire
Brief validated screening tool for identifying chemical sensitivity. The recommended first step before comprehensive QEESI assessment.
Download PDF
MCS Activity & Symptom Tracking Toolkit
Complete toolkit for tracking symptoms and exposures over time, providing the clinical exposure history needed for accurate diagnosis.
Download PDF
TILT Research Program
Evidence-based resources on chemical intolerance, including validated assessment tools and clinical guidance from the University of Texas Health Science Center.
Visit tiltresearch.org
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