Environmental Risk Factors
We evaluate 10 key environmental risk factors that affect the health and quality of life for residents across the United States. Each factor is independently assessed with data from government sources and scientific research.
Air Quality (PM2.5 & Ozone)
Air quality measures the concentration of harmful pollutants in outdoor air that you breathe every day. The two most significant pollutants are fine particulate matter (PM2.5) — tiny particles less than 2.5 micrometers that penetrate deep into the lungs and bloodstream — and ground-level ozone, which forms when sunlight reacts with vehicle and industrial emissions. Poor air quality disproportionately affects children, the elderly, and those with respiratory conditions. Cities in valleys, those with heavy traffic, and areas near industrial operations tend to have the worst air quality. Wildfire smoke has become a growing seasonal contributor to poor air quality across the western United States.
Water Quality
Water quality refers to the safety and cleanliness of the drinking water supply delivered to homes and businesses. Contaminants can enter water from aging infrastructure (lead pipes), agricultural runoff (nitrates, pesticides), industrial discharge, and naturally occurring minerals. Despite federal regulations under the Safe Drinking Water Act, many communities experience water quality violations or detect contaminants at levels of concern. PFAS (forever chemicals), lead from aging service lines, and disinfection byproducts are emerging nationwide issues. Community water quality varies significantly based on source water, treatment methods, and distribution infrastructure age.
Flood Risk
Flood risk measures the likelihood and potential severity of flooding in a given area. Flooding is the most common and costly natural disaster in the United States, causing billions in damage annually. Risks come from river flooding, coastal storm surge, flash floods from heavy rainfall, and urban flooding from overwhelmed drainage systems. Climate change is increasing flood risk in many areas through more intense rainfall events, sea-level rise, and changing storm patterns. Many homeowners are unaware they live in flood-prone areas, and standard homeowner insurance does not cover flood damage.
Toxic Waste (Superfund & TRI Sites)
Toxic waste sites include Superfund sites designated under CERCLA for federal cleanup of the most contaminated locations in America, and Toxics Release Inventory (TRI) facilities that report annual releases of hazardous chemicals to the environment. Living near these sites is associated with elevated health risks from soil, water, and air contamination. The United States has over 1,300 active Superfund sites on the National Priorities List. Additionally, thousands of TRI facilities legally release millions of pounds of toxic chemicals annually. Communities of color and low-income populations are disproportionately located near these hazardous sites.
Wildfire Risk
Wildfire risk has grown dramatically across the United States, particularly in the western states, as climate change extends fire seasons, increases drought conditions, and creates more extreme fire weather. The wildland-urban interface, where development meets undeveloped land, puts millions of homes at direct fire risk. Even areas not directly threatened by flames face severe air quality impacts from wildfire smoke that can travel hundreds or thousands of miles. The annual area burned has more than doubled since the 1990s. Wildfire smoke exposure is emerging as one of the most significant seasonal air quality threats in America.
Earthquake Risk
Earthquake risk affects millions of Americans living near active fault lines across the country. While California and Alaska have the most frequent earthquakes, significant risk also exists in the Pacific Northwest from the Cascadia Subduction Zone, the New Madrid Seismic Zone in the central US, and along the Wasatch Front in Utah. Building codes and construction quality significantly affect earthquake vulnerability. Older buildings and unreinforced masonry structures are most at risk. The potential for catastrophic damage from a major earthquake in a densely populated area remains one of America's highest-consequence natural hazard risks.
Extreme Heat
Extreme heat is the deadliest weather-related hazard in the United States, killing more Americans annually than hurricanes, tornadoes, and flooding combined. Climate change is increasing the frequency, intensity, and duration of heat waves across the country. Urban heat islands amplify temperatures in cities, where dark surfaces and lack of tree canopy can make temperatures 10-20°F hotter than surrounding rural areas. Extreme heat disproportionately affects outdoor workers, elderly residents, those without air conditioning, and people experiencing homelessness. As global temperatures continue to rise, heat risk is expanding into regions historically unprepared for extreme temperatures.
Industrial Pollution
Industrial pollution encompasses the release of harmful chemicals, particulate matter, and waste products from manufacturing, energy production, mining, and processing facilities. While regulations under the Clean Air Act and Clean Water Act have dramatically reduced industrial pollution since the 1970s, many communities still experience elevated pollution levels from active facilities and legacy contamination. Environmental justice research has consistently shown that industrial pollution disproportionately burdens communities of color and low-income populations. Cumulative exposure to multiple industrial sources creates compounding health risks that exceed the impact of any single facility.
Radon Exposure
Radon is a naturally occurring radioactive gas that seeps from the ground into buildings, particularly through foundation cracks, gaps around pipes, and sump pump openings. It is colorless and odorless, making it undetectable without testing. Radon is the second leading cause of lung cancer in the United States, responsible for approximately 21,000 deaths annually. Every home is potentially at risk, regardless of age or condition, though certain geological formations produce more radon than others. The EPA estimates that nearly 1 in 15 US homes has elevated radon levels above the recommended action level of 4 picocuries per liter (pCi/L).
Lead Exposure
Lead exposure remains one of the most significant environmental health threats in America, despite decades of regulations. The primary sources are lead-based paint in homes built before 1978 and lead water service lines delivering drinking water. Approximately 400,000 miles of lead service lines still deliver water across the country. Lead paint is present in approximately 24 million US homes. There is no safe level of lead exposure, and children are particularly vulnerable as lead affects brain development. The Flint water crisis brought national attention to this ongoing crisis, but many communities face similar or worse lead exposure risks.
Why Environmental Risk Factors Matter
Environmental risk factors are the physical, chemical, and biological conditions in your surroundings that can affect your health and well-being. Unlike lifestyle choices that you can control, many environmental risks are determined by where you live. Understanding these risks is the first step toward protecting yourself and your family.
The Environmental Protection Agency (EPA) estimates that environmental factors contribute to a significant portion of preventable diseases in the United States. Air pollution alone is linked to hundreds of thousands of premature deaths annually, while water contamination, toxic waste exposure, and natural hazards like floods and wildfires affect millions more.
Our comprehensive assessment of 10 key risk factors provides a holistic view of environmental conditions across US cities and states. By combining data from multiple government agencies and scientific sources, we help you understand the full picture of environmental health where you live or plan to move.