Sensory Irritation Symptoms
Sensory irritation symptoms involve irritation of the eyes, nose, and throat. Skin irritation is also sometimes considered. While it is clear that numerous VOCs can cause sensory irritation symptoms when airborne concentrations are sufficiently high, at the concentrations typically found in normal buildings the contribution of most indoor VOCs and SVOCs to sensory irritation remains uncertain. Chamber studies with controlled exposures have documented increases in sensory irritation symptoms in people when VOCs are intentionally added to the chamber air, but these studies have used VOCs at airborne concentrations well above the concentrations found in most non-industrial indoor environments [6, 7]. Various estimates have been developed of the airborne concentrations of VOCs needed to provoke sensory irritation. If formaldehyde (discussed below) is excluded, the estimated VOC concentrations needed to provoke sensory irritation generally far exceed the normally observed indoor concentrations of these VOCs [3, 8-10]. In a recent review, Wolkoff et al.  concluded that the VOCs emitted directly to indoors from the aforementioned indoor sources (except from chemical reactions) are unlikely to be present at concentrations sufficient to cause sensory irritation. They suggested that VOCs produced from indoor chemical reactions with ozone might be a source of sensory irritation, that reporting of sensory irritation might be a consequence of VOC-caused odors, and that indoor air may contain currently unrecognized VOCs with the potential to cause sensory irritation.
Although individual VOCs (except possibly formaldehyde and acrolein) are normally not present indoors at concentrations sufficient to cause sensory irritation symptoms, researchers have hypothesized that simultaneous exposures to a large number of indoor VOCs might cause irritation. Consequently, the association of TVOC concentrations with increases in sensory irritation symptoms has been investigated in several multi-building surveys of indoor air quality in which occupants reported health symptoms via a questionnaire. A review  of the relevant literature published before 1996 found that the results of many studies were inconclusive due to methodological or reporting limitations. The review panel provided conclusions from ten cross sectional studies without these limitations. In seven of these studies, there was no association of TVOC concentrations with symptom prevalence rates. One study found an association of higher TVOC with increased SBS symptoms, one study found a possible connection with asthma symptoms, and one study found the TVOC concentration associated with a perception of dry and dusty air. More recently, a cross sectional study in offices [11-13] found that higher TVOC levels (> 666 υg/m3) were associated with 50% to 90% increases in symptom prevalence rates for eye, skin, nose, throat, and mouth irritation symptoms and the increases were statistically significant in many cases; however, higher TVOC levels were generally not associated with objective signs of sensory irritation. In summary, the evidence for an association of higher TVOC concentrations with sensory irritations symptoms is equivocal, with most studies not finding an association. Today, some indoor air researchers believe that measurements of TVOC have minimal value because the composition of individual VOCs within the indoor TVOC mixture varies widely among buildings and because the odor thresholds and potencies of the individual VOCs to cause sensory irritation also vary a great deal [14, 15].
Some of the reported multi-building surveys in office buildings measured airborne concentrations of a broad range of individual VOCs. At least two of these studies found that higher indoor concentrations of some groups of VOCs were associated with increases in sensory irritation symptoms. One of these studies found increased symptoms among occupants of buildings with higher concentrations of VOCs attributed to cleaning products and water-based paints  and the second study found increased symptoms among occupants of buildings with higher concentrations of VOCs attributed to photocopiers and paints .
Numerous studies have investigated the potential of formaldehyde to cause irritation symptoms. Formaldehyde is present in outdoor air, but indoor concentrations are generally well above outdoor concentrations due to the presence of indoor sources including building materials, tobacco smoke, and chemical reactions involving ozone . The studies of irritation from formaldehyde have included chamber studies with controlled short-term exposures to various formaldehyde concentrations, studies of health effects in workers exposed chronically to elevated formaldehyde levels at work, studies of occupants of mobile homes, which tended (at least in the past) to have moderately elevated formaldehyde concentrations relative to typical homes, and animal studies. Various organizations have established guidelines or recommendations (none are legally enforceable limits) for maximum formaldehyde concentrations based on examinations of the scientific literature. Table 1 provides examples of these guidelines, based on sensory irritation effects and on other health effects which are also discussed later in this document.
|Source||Concentration*||Associated Period of Exposure||Health Effect(s)||Reference(s)|
|Based on sensory irritation|
|Health Canada||100 ppb||1 hour||Eye irritation|||
|National Institute for Occupational Safety and Health||100 ppb*||15 minute||*|||
|World Health Organization||81 ppb||30 minute||Sensory irritation|||
|California EPA||75 ppb
44 ppb (proposed)
Eye and airway irritation#
|Based on respiratory and asthma-like symptoms|
|Health Canada||40 ppb (target)||8 hour||Respiratory symptoms in children|||
|California EPA||7 ppb (proposed)||Repeated 8-hour||Asthma-like respiratory symptoms|||
|Based on cancer risk|
|National Institute for Occupational Safety and Health||16 ppb||8 hour||Nasal cancer|||
* Associated health effect not unambiguously identified but likely to be irritation effect given the associated 15 minute exposure period
# and nasal obstruction and nasal lesions
To place the formaldehyde guidelines based on sensory irritation in context, one must consider how they relate to indoor formaldehyde concentrations. From a review in 2003 of available data collected since 1990  from convenience samples of U.S. homes (samples collected in homes convenient to researchers without any assurance that the resulting sample of homes is representative of all U.S. homes), about half had a formaldehyde concentration above 17 ppb and 10% of homes had a concentration greater than 37 ppb. Because a small fraction of homes had much higher concentrations, the estimated average concentration in a U.S. home was 55 ppb. In a survey of new homes in California (new homes tend to be more air tight and to have stronger formaldehyde sources), half of houses had a formaldehyde concentration greater than 31 ppb and 25% had a concentration greater than 60 ppb . The outdoor concentrations of formaldehyde ranged from 0.6 to 2 ppb. From these data, it is clear that formaldehyde concentrations in most homes exceed the repeated 8-hour guideline of 2 ppb established by the California Environmental Protection Agency (EPA) to prevent sensory irritation (and nasal effects) but that few homes are likely to have concentrations exceeding the higher guidelines established by other organizations to prevent sensory irritation.