Chemical sensitivity is not considered an allergic reaction because it does not involve the release of IgE (immunoglobin E) antibodies, histamine, or other chemicals by the immune system. However, reactions to certain chemicals may cause reactions similar to those experienced with allergies.
Chemicals that cause sensitivity may include synthetic and natural substances found in:
Poorly ventilated wood-burning stoves
Inhaled ozone and nitrogen dioxide
Sulfur dioxide inhalation
Natural outdoor pollution, such as dust storms, forest fires, or erupting volcanoes
Man-made outdoor pollution: vehicle exhaust, petroleum refining, and fossil fuel combustion