VOCs from Indoor Chemical Reactions and Health
Chemical reactions indoors have been shown to occur between “oxidizing” compounds such as ozone and various common indoor compounds such as terpenes that are easily oxidized, in air or on surfaces such as carpets, often through the formation and reaction of hydroxyl radicals . Byproducts of these indoor air chemical reactions (e.g., formaldehyde, acrolein, hydroperoxides, fine and ultrafine particles) have been hypothesized to cause sensory irritation of eyes and airways or skin irritation [2-4]. Indoor chemical reactions from outdoor ozone that has entered buildings, resulting in oxidation products with known or suspected health effects, have been hypothesized to contribute to the adverse health effects associated epidemiologically with outdoor ozone . Formaldehyde is one of the products of such reactions, but emissions from other sources of indoor formaldehyde will usually greatly exceed formaldehyde production by chemical reaction. Outdoor air is normally the major source of indoor ozone, although ozone generators (marketed as air cleaners that intentionally produce ozone), electronic air cleaners (that unintentionally produce ozone as a by-product), and some types of office equipment can be additional sources of ozone .
Wolkoff et al.  estimated the potency of a set of five common terpene reaction byproduct chemicals, using a mouse bioassay, for three adverse respiratory effects: acute upper airway sensory irritation, airflow limitation, and pulmonary irritation. Extrapolation to human effect levels found no likely substantial contribution to sensory irritation or airflow limitation, and no evidence of pulmonary irritation at indoor levels. Also, Wolkoff et al.  had previously shown that even repeated exposures to indoor chemistry byproducts did not produce increased health effects.
However, Wolkoff et al.  suggested that steps be taken to minimize the formation of two of the studied compounds, 3-isopropenyl-6-oxo-heptanal (IPOH) and 4-oxo-pentanal (4-OPA), because of their relatively high estimated sensory irritation potencies. Effective steps to reduce their production might include limiting indoor concentrations of ozone and also of limonene or other precursors. For reducing the production of 4-OPA specifically, precautionary actions might include cleaning to remove human and animal skin debris, and preventing crowded, poorly ventilated space. Still, prior research findings suggest that other products of indoor chemical reactions may cause sensory irritation or inflammatory reactions, in ways not yet understood [3, 7-9]. Overall, the current evidence is too sparse to draw conclusions about the health consequences of indoor chemical reactions.
5. Wolkoff, P., et al., Human reference values for acute airway effects of five common ozone-initiated terpene reaction products in indoor air. Toxicol Lett, 2013. 216(1): p. 54-64. https://dx.doi.org/10.1016/j.toxlet.2012.11.008 [doi].
8. Klenø, J. and P. Wolkoff, Changes in eye blink frequency as a measure of trigeminal stimulation by exposure to limonene oxidation products, isoprene oxidation products and nitrate radicals. International archives of occupational and environmental health, 2004. 77(4): p. 235-243.