Exposure to biological sources associated with increased risk of chemical intolerance

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Exposure to biological sources associated with increased risk of chemical intolerance

What initiates chemical intolerance (CI)? In a recently published survey of thousands of US adults, respondents most often cited exposure to biological sources, such as mold and algal blooms, and/or fossil fuels, their combustion products, and synthetic chemical derivatives such as pesticides, plastics, and persistent organic pollutants .

It’s an issue in the news because toxic mold from moisture left behind by flooding from Hurricane Idalia can cause serious health problems for people who suffer from chemical intolerances. This mold can also initiate the condition in some individuals.

Everyone should avoid prolonged exposure to mold whenever possible. Research is increasingly showing that toxic mold is much more dangerous than previously thought.”

Claudia Miller, MD, MS, Research Physician, University of Texas Health Science Center at San Antonio

In the survey published in Environmental Sciences Europe, 17.5% of participants who attributed their illness to a triggering event cited mold exposure as the suspected cause of their chemical intolerance. CI is estimated to affect as many as 20 percent to 30 percent of Americans, said Miller, the study’s senior author.

Participants were also asked about antibiotic use. According to the results, prolonged courses of antibiotics were associated with an increased risk of CI.

The survey data also showed that with each additional initial exposure that respondents could recall, the odds of reporting CI nearly tripled.

“With climate change contributing to more severe storms and more intense flooding worldwide, the threat of toxic mold is likely to increase dramatically in the near future,” Miller said. “Since exposure to mold is known to be a major trigger, the likelihood of more and more chemically intolerant people is also unfortunately increasing.”


The study adds to the understanding of how a two-step disease process called TILT (toxicant-induced loss of tolerance) begins. The study asked 10,981 people to report their own perceptions of the events that started the downward spiral through TILT and toward chemical intolerance.

“TILT can develop quickly, such as after exposure to pesticides, or gradually if someone works or lives in an environment like a moldy building,” Miller said. She first offered TILT in 1996 and is a professor emeritus of family and community medicine at UT Health San Antonio.

Unknown origin

“Initial events usually go unrecognized and therefore unreported, leaving triggers and symptoms as the only documented components,” Miller said. “This has thwarted our understanding of the actual causes of TILT.”

Participants completed an 80-question online survey called the Personal Exposure Inventory. It includes items related to individuals’ medical diagnoses and personal exposures, including antibiotic use.

Chemical intolerance was assessed using the Quick Environmental Exposure and Sensitivity Inventory (QEESI©), developed by Miller 25 years ago. It is a validated, self-administered questionnaire that is now used worldwide to differentiate individuals with CI from the general population. One fifth of respondents met the QEESI criteria for chemical intolerance.

Toxic mold

Exposure to mold was the most frequently cited initiating event on the personal exposure list. “In recent years, global warming has led to more rainfall, flooding, hurricanes, roof leaks and water intrusion, leading to increased indoor mold growth,” said report co-author Raymond F. Palmer, Ph.D., biostatistician and professor in Family and Community Medicine at UT Health San Antonio.

Mold was followed in order by pesticide exposure (cited by 13.8% of respondents), medical/surgical procedures (12.6%), remodeling/new construction (12.0%), fires/combustion products (7, 2%) and breast implants (1.8%).


Respondents answered questions related to how many courses of antibiotics they had completed for specific types of infections. Antibiotics prescribed for infections categorized as skin, tonsil, gastrointestinal, prostate, sinus, wound, and pneumonia were most strongly associated with chemical intolerance.

“Our search for the underlying causes of CI represents a much-needed addition to the CI/TILT literature, whose primary focus has been on the triggers that produce CI symptoms on a day-to-day basis, without attempting to determine what initiated TILT,” Miller said.

“Cohesive Narrative”

“Taken together, our data support the idea that the individual reporting multiple symptoms, multiple intolerances, and recurrent infections, as well as a history of exposure events, share a cohesive narrative that points to physiological (as opposed to psychosomatic) explanations for their often confusing complaints,” she said.

Although some exposures, such as medical/surgical procedures, may be difficult to avoid, reducing contaminant exposures associated with pesticide use, new construction/remodeling, and mold is possible and should be a focus of prevention efforts of future CI/TILT, the authors write.

Digging in

Finally, they encourage practitioners who see patients with medically unexplained symptoms -; currently one in four primary care patients -; to consider administering the QEESI. “‘Tilted’ individuals who report brain fog, memory, mood, and concentration problems often receive referrals to psychiatrists, psychologists, or social workers who examine their psychosocial environment but do not ask about changes in their actual -; physical and chemical -; environment,” Miller said. “If initial exposures such as pesticides, toxic molds, implants and combustion products are not stopped, sensitivities can spiral out of control.”

Teaching in schools of medicine, public health, architecture and engineering has not kept up with these toxic substances, many of which are new to the planet since World War II, Miller noted. That’s exacerbated by energy conservation efforts that have increased exposure to toxic substances in indoor air, she said.

Marilyn Brahman Hoffman

In their acknowledgments, the authors “thank the Marilyn Brahman Hoffman Foundation for generously funding this study and Marilyn Hoffman for her prophetic bequest prioritizing the study of toxicant-induced loss of tolerance. We are deeply grateful to the patients who participated in this groundbreaking study.”

Hoffman’s bequest specifies the TILT research. “She herself suffered terribly from intolerances to chemicals, food and drugs, but especially from family members and her doctors not believing her,” Miller said. “She was a citizen scientist who read all my articles and the book Chemical Exposures: Low Levels and High Stakes, co-authored with Nicholas Ashford, PhD, JD, of MIT.

“More than anything, Ms. Hoffman wanted to discover the biomechanism for TILT,” Miller said. “She knew it was essential to help patients like her. Her bequest led to the publication of the biomechanism for TILT in a series of articles over the past two years in Environmental Sciences Europe, a journal read by regulatory toxicologists worldwide.”

If you suspect you or a loved one has developed chemical intolerance or TILT, take this short, three-question yes-or-no screening test called the BREESI. A positive answer to any of the questions should lead to completion of the more extensive, validated diagnostic questionnaire, the QEESI or Quick Environmental Exposure and Sensitivity Inventory. People who score high on the QEESI are considered likely to have a chemical intolerance and are encouraged to share the information with their healthcare providers.


University of Texas Health Science Center at San Antonio

Journal reference:

Miller, CS, et al. (2023) What initiates chemical intolerance? Findings from a large survey of US adults. Environmental Sciences Europe. doi.org/10.1186/s12302-023-00772-x.

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