Mast cell activation may explain many cases of chemical intolerance

Claudia S. Miller, Raymond F. Palmer, Tania T. Dempsey, Nicholas A. Ashford, Lawrence B. Afrin

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


Background: This paper explores the relationship between chemical intolerance (CI) and mast cell activation syndrome (MCAS). Worldwide observations provide evidence for a two-stage disease process called toxicant-induced loss of tolerance (TILT) as a mechanism for CI. TILT is initiated by a major exposure event or a series of lower-level exposures. Subsequently, affected individuals report that common chemical inhalants, foods, and drugs (i.e., various xenobiotics) trigger multi-system symptoms. Purpose: To determine whether MCAS provides a plausible biological mechanism for CI/TILT. Methods: Using the validated Quick Environmental Exposure and Sensitivity Inventory (QEESI), we compared patients diagnosed with MCAS (n = 147) to individuals who reported chemical intolerances (CI/TILT) following various exposures (n = 345) and to healthy controls (n = 76). Using ANOVA, we compared QEESI scores across groups. Clinical scores for the MCAS patient group were used to predict CI status using logistic regression. Results: More than half (59%) of the MCAS group met criteria for CI. A logistic regression model illustrates that as the likelihood of patients having MCAS increased, their likelihood of having CI/TILT similarly increased, to a near-perfect correspondence at the high ends of the QEESI and clinical MCAS scores. Symptom and intolerance patterns were nearly identical for the CI and MCAS groups. Discussion: We present data suggesting that xenobiotic activation of mast cells may underlie CI/TILT. The strikingly similar symptom and intolerance patterns for MCAS and TILT suggest that xenobiotics disrupt mast cells, leading to either or both of these challenging conditions. Faced with patients suffering from complex illness affecting multiple organ systems and fluctuating inflammatory, allergic, and dystrophic symptoms, clinicians can now ask themselves two questions: (1) Could MCAS be at the root of these problems? (2) Could environmental exposures be driving MC activation and mediator release? Increasing our understanding of the connection between TILT and MCs has the potential to expose a new link between environmental exposures and illness, offering new opportunities for improving individual and public health. Conclusion: The close correspondence between QEESI scores and symptom patterns for MCAS and TILT patients supports xenobiotic-driven mast cell activation and mediator release (i.e., MCAS) as a plausible unifying biological mechanism for CI/TILT, with profound implications for medicine, public health, and regulatory toxicology.

Original languageEnglish (US)
Article number129
JournalEnvironmental Sciences Europe
Issue number1
StatePublished - Dec 2021


  • Allergies
  • Chemical intolerance
  • Drug intolerance
  • Environmental exposure
  • Food intolerance
  • Mast cell
  • Mast cell activation syndrome
  • Regulatory toxicology
  • Toxicant-induced loss of tolerance (TILT)
  • Xenobiotics

ASJC Scopus subject areas

  • Pollution


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