Recommendations to spend more time indoors or
make buildings “tighter” to reduce penetration of ambient
pollutants are further complicated by variable indoor sources of air pollutants and the theoretical net risk from
the different air pollutants that may be encountered
indoors from both indoor and outdoor sources (Figure 1).
Staying indoors and decreasing home ventilation reduces
personal exposures to pollutants of outdoor origin, but at
the same time may potentially increase personal exposures
and health risks from a variety of indoor-generated
primary and secondary air pollutants, including volatile
organic compounds from consumer products and building
materials, and nitrogen oxides, carbon monoxide and
particulate matter from indoor combustion activities such as
cooking, wood burning, and smoking tobacco products. For
example, Huang et al. [2014] reported that levels of indoor
PM were associated with decreased heart rate variability
(HRV) among housewives. After adjustment for confounders,
an interquartile range increase in PM2.5 was associated with
statistically significant 1.25-4.31% decreases in standard
deviation of normal to normal (SDNN) and 0.12-3.71%
decreases in root mean squared of successive differences
(rMSSD) HRV, and these effects were stronger during
stir-frying, cleaning with detergent, and burning incense (12).