Pollution in the environment can have significant effects on human health. However, some individuals, or even groups of people, are more vulnerable to health risks from exposure to environmental contamination. Many variables directly or indirectly influence these health effects. For example, air pollutants can trigger asthma among the very young and very old, as well as in individuals who have a family history of asthma, or aggravate existing respiratory and cardiac conditions. Many environmental health risks are preventable or can be mitigated. Public access to a wide range of information—such as data on pollutant emissions and ambient air quality conditions—is instrumental to reduce the risk of exposure for individuals and vulnerable communities.