Characterizing Indoor Exposures to Advance Exposome Research

Post Date: July 9, 2026

Expiration Date: July 9, 2028

NIH is interested in advancing our understanding of the indoor environment as a critical component of the exposome by investigating exposure pattens across different indoor environment settings, identifying major sources of exposure, and quantifying their contributions to the overall exposure and health burden.

Background:

The exposome, which describes the totality of environmental exposures an individual experiences from conception to death, provides a comprehensive framework for understanding how the environment impacts human health. Within this framework, exposures in the indoor environments, where people spend most of their time, remain an understudied component in exposome research. These indoor environments span residential, commercial, industrial, and institutional settings and pollutants can be trapped and concentrated. On average, people spend 80-90% of their time indoors, making indoor exposure a primary determinant of an individual’s total exposure.

Thousands of contaminants are found indoors due to direct chemical emission from building materials, furnishing, stoves, cleaning and personal care products, office equipment as well as biological sources such as mold and pets. Oftentimes, the levels of indoor pollutants exceed those in the outdoor environment (e.g., PCBs from paint, formaldehyde from furniture, and NO2 from gas stoves). Additionally, indoor surfaces and dust can absorb and store chemicals, resulting in chemical reactions and persistent release of pollutants into the air. Exposure to indoor pollutants is associated with a wide range of adverse health outcomes across the lifespan, especially in young children and older adults who tend to spend more time indoors. Capturing and integrating exposures such as airborne pollutants (e.g., particulate matter, volatile organic compounds (VOCs)), biological agents (e.g., allergens, microbes), and physical factors (e.g., ventilation, lighting, noise, thermal conditions) across varied indoor settings is critical for understanding the cumulative effects of the exposome in shaping human health. Yet, incorporating indoor exposures into exposome research faces several methodological and conceptual challenges:

Indoor environmental exposures are complex mixtures that vary across building types (residential, non-residential, mixed-use development, etc.).

Accurate assessment tools are lacking for measuring indoor exposure beyond a few commonly studied pollutants (e.g., particulate matter, ozone, certain VOCs).

Most health studies on indoor exposure conducted so far evaluate single exposures or single classes of exposures, limiting the understanding of mixture effects, secondary products from chemical reactions, and cumulative health effects.

Indoor exposures may have multiple sources, including both indoor emissions and outdoor origins and are impacted by human behaviors, ventilation sources, and proximity to the source of exposures.