Allergy, Asthma, and Related Respiratory Symptoms
The associations of indoor VOCs, SVOCs, and their sources with allergy and asthma outcomes and lower respiratory symptoms indicative of asthma have also been investigated. Mendell reviewed the relevant scientific literature from studies performed in sets of homes [26]. This review determined that several, but not all, studies found moderate to strong increases in respiratory and allergic health effects among children in homes with higher concentrations of selected VOCs or SVOCs, including formaldehyde and some types of phthalates (softening agents for some plastics), or in homes with larger amounts of some VOC or SVOC sources, such as particleboard, plastics, and recent paint. The types of studies reviewed can identify associations or correlations of health effects with higher VOC concentrations or with likely VOC sources, but cannot prove that the VOCs are definitely causing the health effects. A recent review by the California EPA [23] considering a broader set of evidence, e.g., studies in homes, studies of workers, chamber exposure studies, animal studies, and research on the toxicological mechanisms, also identified a linkage of formaldehyde with increases in asthma-like respiratory symptoms, which is the basis for the proposed 7 ppb guideline in Table 1. However, a third review [27], relying more on studies using animals and short-term chamber studies with humans, found no conclusive evidence that indoor VOCs (excluding formaldehyde) are associated with airway allergies or asthma. More recently, a high frequency of use of household cleaning sprays was found to be associated with a 40% increase in wheeze, with a 50% increase in asthma symptoms or medication use, and with approximately a 100% increase in incidence in physician-diagnosed asthma [28]. These cleaning sprays are known to emit various types of VOCs. In summary, additional research is needed before firm conclusions can be drawn about the effects of indoor VOCs or SVOCs on allergy or asthma. The existing evidence of risks is sufficient to indicate that such research is a high priority.