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The occurrence of asthma has doubled in the United States in the last two decades, although recent evidence indicates that rates may now have leveled off. Much of this increase has been seen in African-Americans and children, especially inner-city children, but no one knows why. Science has not yet answered with certainty what the underlying causes of asthma are, or what triggers an attack. Some substances in indoor air are considered to be asthma triggers. But there are still few answers.
Some have speculated that the presence of phthalates in polyvinyl chloride, commonly called PVC or vinyl, might be the cause, or one of the causes, of the increase in asthma. Specifically, one article said that "PVC materials and textile wall materials used in the home environment are possible determinants," and that "possible direct causal agents could be plasticizers emitted from PVC plastic materials." The article offered no hard evidence to support these suggestions, which are carefully conditioned with words like "possible," or "could." Another study claimed to see an association between levels of various phthalates in household dust and allergy-related illnesses, including asthma, although that report is flawed and of questionable reliability (for more information about this study, see www.phthalates.org/mediacenter/panelstatement.asp?ID=55).
Asthma is considered mainly to be an allergic disease in which the airways become inflamed and constricted. Most of the agents associated with asthma are strong allergens or irritants (e.g., cat dander, house dust mites, and tobacco smoke), although other factors that cause airways spasms (e.g., cold air, or exercise) can also trigger asthmatic attacks. Testing has not shown phthalates to be allergens nor has testing shown them to be strong irritants, so allergy science tells us that it is unlikely that they could act as triggers for an asthmatic attack.
In research published in 2003, various phthalates were painted on the skin of mice, and other known allergens were also applied. The known respiratory allergens stimulated the production of specific marker proteins that are associated with allergic illness; the phthalates did not. Because the tested phthalates did not show the types of immune responses associated with respiratory allergy, allergy science would tell us that they would be unlikely to induce asthma by an allergic response. A study published in 2004 by a team including Danish researcher Gunner Nielsen concluded that "Based on a worst case scenario in the general population, no airway irritation is expected from non-occupational levels of MEHP originating from DEHP." Even more recent research to be submitted to the Society of Toxicology in 2005 (abstract in press) reports that DEHP painted on the skin of rats already sensitized with a known allergen did not magnify the allergic effect.
Based on these studies, it is believed that phthalates do not cause, and are not likely to exacerbate, asthma.
Phthalates are bound in the molecular matrix of vinyl. They are relatively heavy molecules and have very low volatility, meaning that they tend not to evaporate. The ranges of airborne concentration of phthalates in a room with vinyl floor and wall covering have been measured to be extremely low (ranging from undetectable to just a few millionths of a gram per cubic meter of air). In inhalation studies on rodents, concentrations more than a million times greater than ambient levels have been required to result in an irritation reaction in rodents. Thus, basic science makes it unlikely that inhalation of phthalates could be an asthma trigger in humans.
Questions have been raised whether PVC fragments containing phthalates might be freed by the wear and tear on vinyl flooring and become part of the dust in a household. The answer is possibly yes, but such wear is slight even over a period of years. And these PVC particles would make up just a small fraction of household dust, which also contains dust mites, dead skin, molds, surface soils, and many other allergy-inducing components. Furthermore, there is no consistent evidence that the phthalate portion of PVC dust particles is "bioavailable" – that is, that it can be adsorbed and digested by the body.
New research conducted in Germany and published in 2004 by Becker et al. compared the levels of the phthalate DEHP in household dust to the level of metabolites of DEHP in 254 children. The purpose was to see whether higher concentrations of DEHP in the dust corresponded with higher exposure levels in the children, which would add support to the hypothesis that phthalates in dust could contribute to the induction of childhood asthma. But the study authors reported that no correlation could be found. A more recent assessment (the abstract is in press) reported that the potential human exposure levels from phthalates in dust is between 100,000 and 1,000,000 times lower than levels in rodents that produced minimal effects indicative of respiratory inflammation.
The Institute of Medicine (IOM), an arm of the National Academy of Sciences, has evaluated possible asthma causes and triggers. A report published in 2000 titled "Clearing the Air: Asthma and Indoor Air Exposures," stated that there is "inadequate or insufficient information" to support the idea that plasticizers present a problem for asthma sufferers.
Last Updated: February 11, 2005
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