- In animal tests, phthalates do not generate the types of immune responses associated with respiratory allergy, and are unlikely to induce asthma by an allergic response.
- Levels of phthalates in household dust are between 100,000 and 1,000,000 times lower than levels that produced minimal respiratory effects in rodents.
Some researchers have studied possible links of phthalates to indoor air-quality issues and asthma. But phthalates are tightly bound in the structure of vinyl, they have very low volatility, which means they do not tend to evaporate, and they have little to no odor. Therefore, phthalates do not likely contribute to poor indoor air quality or asthma.
Asthma cases have doubled in the United States in the last two decades, although 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 these populations are more affected. 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 many questions remain.
Asthma Triggers
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); but 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. As a consequence, it is unlikely that phthalate exposure could act as a trigger for asthmatic attacks.
Furthermore, phthalates do not easily migrate out of flexible vinyl products because they are physically trapped in the molecular matrix of flexible vinyl. They are relatively heavy molecules and have very low volatility, which means they tend not to evaporate. The ranges of airborne concentration of phthalates in a room with vinyl floor and wall coverings, for instance, 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, further indicating that it is unlikely that inhalation of phthalates could be an asthma trigger in humans.
Questions have been raised about whether polyvinyl chloride (PVC) fragments containing phthalates might be freed by the wear and tear on vinyl flooring and become part of the dust in a household. Such wear, however, 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”—meaning it can be absorbed and digested by the body.
Research on Phthalates
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, 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.” Other research submitted to the Society of Toxicology in 2005 reported that DEHP painted on the skin of rats already sensitized with a known allergen did not magnify the allergic effect. In 2009, work published by Dearman concluded that “the doses of (BBP—used in vinyl flooring) encountered in the home environment are unlikely to be a major factor contributing to the increased incidence of asthma and allergy in the developed world.”
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. The study’s authors reported that no correlation could be found between DEHP levels in dust and metabolite levels in the children, which casts considerable doubt on the possible contribution to incidence of childhood asthma. Another assessment 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, also evaluated possible asthma causes and triggers. A report published in 2003 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.
Based on these studies, it is believed that phthalates do not cause, and are not likely to exacerbate, asthma.
You can learn more about asthma and indoor air quality from EPA's website:
An Introduction to Indoor Air Quality (IAQ).
