The exposome comprises all environmental exposures that a person
experiences from conception throughout the life course. Here we
review the state of the science for assessing external exposures
within the exposome. This article reviews (a) categories of
exposures that can be assessed externally, (b) the current state
of the science in external exposure assessment, (c) current
tools available for external exposure assessment, and (d)
priority research needs. We describe major scientific and
technological advances that inform external assessment of the
exposome, including geographic information systems; remote
sensing; global positioning system and geolocation technologies;
portable and personal sensing, including smartphone-based
sensors and assessments; and self-reported questionnaire
assessments, which increasingly rely on Internet-based
platforms. We also discuss priority research needs related to
methodological and technological improvement, data analysis and
interpretation, data sharing, and other practical
considerations, including improved assessment of exposure
variability as well as exposure in multiple, critical life
stages