The study, done at two Texas family medicine practices, screened patients for symptoms of "chemical intolerance," also known as multiple chemical sensitivity.

It's a controversial diagnosis, and there's no agreement on the cause - or that it even should be considered a disorder unto itself.

But there is a standard screening questionnaire that's been used in studies and in some doctors' practices. It asks people about whether they feel sick when they're around various smells and chemicals -- like gasoline, paint, perfumes, cleaning products or insecticides -- and how bad the symptoms are.

Using that questionnaire, researchers found that 20 percent of 400 patients they screened met the criteria for chemical intolerance.

Most studies on chemical intolerance have focused on higher-income, white people. But patients in this study were largely lower-income and Hispanic.

So the findings give an idea of the prevalence of such symptoms in an understudied group, according to lead researcher Dr. David A. Katerndahl, of the University of Texas Health Science Center at San Antonio.

He said lower-income Americans may, in theory, be more likely to have chemical intolerance since they more often have jobs that would routinely expose them to chemicals.

In an interview, Katerndahl acknowledged that chemical intolerance, as a diagnosis in and of itself, is controversial.

"Some doctors will never believe it exists," he said. But there has been growing acceptance of it among primary care doctors, he added.

And these new findings, Katerndahl said, help confirm what a lot of doctors have suspected: that chemical intolerance often goes hand-in-hand with mental health disorders.

Of 81 patients with chemical intolerance, 85 percent reported having symptoms of major depression in the past month. Another 78 percent had symptoms of an anxiety disorder. That compared with 33 percent and 21 percent, respectively, among patients free of chemical intolerance.

But that doesn't necessarily mean the mental health problems caused the chemical sensitivities, according to Katerndahl.

"We don't know why this association exists," he said. It's possible, for example, that some people have an underlying vulnerability to both mental health disorders and chemical sensitivities.

Or, Katerndahl said, some people might become depressed or anxious because of their chemical intolerance symptoms - which can include headaches, dizziness, upset stomach or breathing problems.

Of the 81 study patients who screened positive for chemical intolerance, one-quarter had previously been diagnosed with it, Katerndahl's team found.

That suggests the problem "often goes unrecognized," the researchers report in the Annals of Family Medicine.

According to Katerndahl, doctors might want to screen for chemical sensitivities in certain situations, such as when patients complain they can't seem to tolerate a range of medications.

"If you can figure out if you're sensitive to certain chemicals," Katerndahl said, "then you can try to engineer your life to avoid them."

And if you think you're overly sensitive to certain chemicals and your regular doctor cannot help, he added, you might want to get a referral to an allergist.

SOURCE: bit.ly/MkAv8K Annals of Family Medicine, July/August 2012.

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