Multiple chemical sensitivity has many alternative names, including chemical injury syndrome, twentieth century syndrome, toxic injury, environmental illness, environmental sensitivity, and idiopathic environmental intolerance. All of these different terms describe a chronic condition which is characterized by symptoms such as nausea, heart palpitations, aching joints, headache, and itchy eyes. It is believed that these symptoms are the result of low-level chemical exposure in people who have increased sensitivity to environmental toxins such as cigarette smoke, perfumes, industrial chemicals, petroleum products, and pesticides.
For an individual to be diagnosed with multiple chemical sensitivity, he or she must have symptoms which conform to six diagnostic criteria. First, the individual must have had the condition for a certain amount of time. His or her symptoms must be reproducible, meaning that exposure to chemicals on different occasions produces similar symptoms. In addition, the symptoms must be reproducible at low levels of exposure, and symptoms must cease or lessen when exposure to the chemicals ceases. For the condition to be diagnosed, the individual must also be sensitive to several different types of chemicals.
The final diagnostic criteria for multiple chemical sensitivity is the range of symptoms that the individual experiences. The symptoms must involve multiple organ systems; for example, the digestive system and the respiratory system. Possible symptoms may include headache, earache, itchy eyes, runny nose, itchy throat, sleepiness, drowsiness, or mental confusion, extreme anxiety, panic attacks, heart palpitations, abdominal cramps, diarrhea, nausea, and upset stomach.
While most people with multiple chemical sensitivity attribute their symptoms to chemical intolerance and hypersensitivity, some medical experts believe that that this is not a valid diagnosis. In one research study, half the participants were found to have other disorders, such as depression or panic disorder, rather than suffering from multiple chemical sensitivity. In blind trials of triggering chemicals, it has been found that many people are triggered not by chemicals, but by odors, suggesting that their symptoms may be partially psychosomatic.
Due to results such as these, the World Health Organization and many other global and regional associations do not recognize environmental sensitivity as a real condition. In addition to theories about physiological causes and misdiagnosis, some experts believe that the so-called twentieth century syndrome may be a type of allergy rather than a chemical intolerance. To date, critics of the diagnosis maintain that there is no scientifically sound theory to account for the disease.
The most recent research to suggest a cause showed that some people with the disease have a specific genetic mutation that may play a role. The mutation is in a protein involved in metabolic pathways that break down toxins, and the research suggests that the mutated protein may metabolize certain toxins differently. This type of mutation may account for certain types of chemical sensitivity, and may also play a role in diseases such as fibromyalgia and chronic fatigue syndrome.