Senses and Sensitivity

William Cain, a professor of surgery, Enrique Cometto-Muniz, an associate research scientist, and colleagues at the Chemosensory Perception Laboratory at the University of California at San Diego are conducting extensive research on the sense of smell and sensory irritation from chemicals in the indoor environment. Cometto-Muniz says the goal of the research is to provide further insight into the sense of smell so that it can be as well understood as the visual and aural senses. "We know very well the electromagnetic spectrum to which the eye responds and the vibrational spectrum to which the ear responds, but we don't know the chemical spectrum to which the nose responds," he says.

Cain says an important issue to consider in investigating the effects of fragrance on the body is differentiating between psychological irritation from unpleasant chemical odors and actual sensory irritation from chemicals. Because of the strong tie between the sense of smell and emotion, researchers say foul odors emitted by certain chemicals can provoke people to believe their health is being impacted when, in fact, the offending substance may be benign.

Cain and Cometto-Muniz are working to establish the odor and irritant thresholds of chemicals--at what level a chemical first is an odorant and then becomes an irritant. Identifying such thresholds will aid in distinguishing the psychological response to odor from measurable nasal and eye irritation. The involvement of anosmics, or people who have no sense of smell, in the studies allows for the "perfect opportunity to differentiate what is a trigeminal response from an olfactory response," says Cometto-Muniz.

So far, the group has successfully established the threshold levels of physiological irritation for several chemical mixtures. Their research has indicated that the higher the number of chemicals being combined, the lower their individual levels need to be to cause sensory reactions. Areas they plan to further investigate include chemical mixtures, as well as the role of time in sensory irritation and sense of smell. Cometto-Muniz says that when a person is exposed to an odor, the sensation appears to diminish over time as the person seemingly adapts to the odor, while sensory irritation occurs in an opposite manner--as time passes, irritation increases. While there are still many questions about how long-term sensory irritation may affect health, Cometto-Muniz points out that "sensory irritation is there to warn us that continued exposure could potentially be dangerous."

One of the few studies that has looked at the effects of inhalation of specific fragrance chemicals and perfumes was conducted at the private Anderson Laboratory in West Hartford, Vermont, by Rosalind Anderson, founder and owner of the laboratory, and Julius Anderson, vice president. The goal of the study was to determine whether fragrance products can produce acute toxic effects in mammals. The Andersons exposed laboratory mice to five fragrance products--four colognes and one toilet water. The mice breathed the emissions of the products for 1 hour and then were tested using the ASTM-E-981 method to evaluate sensory irritation and pulmonary irritation, as well as a functional observational battery to look for changes in the nervous system function.

The study, published in the March-April 1998 issue of Archives of Environmental Health, showed that the emissions of the fragrances produced various combinations of sensory irritation, pulmonary irritation, decreases in expiratory airflow velocity, and alterations of the functional observational battery indicative of neurotoxicity. Neurotoxicity was more severe after mice were repeatedly exposed to the products.

The Andersons say the findings indicate that some fragrance products produce toxic effects in at least one mammalian species. In the study's conclusions, they wrote, "Collectively, the experimental data and chemistry predict that some humans exposed to these fragrance products might experience some combination of eye, nose, and/or throat irritation; respiratory difficulty; possibly bronchoconstriction or asthma-like reaction; and central nervous system reactions (e.g., dizziness, incoordination, confusion, fatigue). The results of our study might help explain why some individuals report an intolerance to [fragrance products] and why some [fragrance products] can exacerbate airflow limitation in some asthmatics."

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