The Japanese cedar was never known to cause allergic rhinitis in Japan until the 1960s even though the tree had been indigenous to Japan for more than a million years. Recognition of cedar-induced rhinitis and an increase in cases in Japan coincided with lenient regulation of diesel exhaust and increased numbers of diesel vehicles in that country.

What does cedar (really a juniper) allergy have to do with diesel exhaust? Exposure to petrochemicals such diesel exhaust, can lower a person’s tolerance for “natural” substances such as pollen, mold, dust mites and animal dander, leading to allergic reactions. Researchers in Japan have confirmed that exposing mice to diesel exhaust increases their IgE production, the immunoglobulin associated with allergy.

What does this have to do with TILT, or Toxicant-induced Loss of Tolerance? People who become chemically intolerant, or TILTed, frequently report amplified allergic responses. This relationship may help explain the rise in allergic rhinitis in Japan. It explains why the QEESI, or Quick Environmental Exposure and Sensitivity Inventory, asks about a person’s exposures to diesel exhaust and any associated heightened allergic responses.

I know how potent cedar pollen can be. I live in Central Texas, on the edge of the scenic Texas Hill Country. Despite its beauty, the Hill Country has hundreds of thousands of Texas Mountain Cedars that shed notoriously allergenic pollen. From December to February, the pollen causes such severe symptoms that sufferers call it “cedar fever.”