Children’s Unique Vulnerabilities to Environmental Hazards

Children are not simply little adults. They progress through distinct stages of growth, each with unique biology, activity patterns, and behaviors that shape their vulnerabilities. These differences influence how environmental exposures affect their health. All people go through a sequence of developmental life stages; viewed this way, children are not a distinct subpopulation.

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Why Children May Be at Greater Risks than Adults

Children may be at greater risk to environmental pollutants than adults due to differences in behavior and biology. In addition to immediate impacts, some early‑life exposures may lead to potential lifelong health impacts, and some effects may not appear until adolescence or adulthood; in certain cases, effects may also arise in later generations.

Biological Differences

Children eat more food, drink more water, and breathe more air in proportion to their body weight than adults, which can increase exposure to environmental pollutants. Because their organs, and systems – including the brain, lungs, liver, kidneys, nervous system, and immune system – are still developing, environmental pollutants may be absorbed differently and cleared less effectively. The timing of exposure to pollutants is critical in protecting human health; children may be more or less sensitive than adults at equivalent exposure levels.

For example, children have:

• A blood-brain barrier that isn’t fully developed.
• Less effective filtration in the nose and lungs.
• More permeable skin.
• Immune systems that are still maturing, reducing ability to fight infections and maintain overall health.

Children go through critical windows of susceptibility, periods during fetal development and early childhood, when exposure can cause lasting, potentially lifelong, heath effects. These windows occur when a developing organ or system is undergoing rapid change and may be especially sensitive; the same exposure outside that window may have a smaller or different effect. Short‑term exposures during these windows can lead to lasting changes even after the exposure ends. Some impacts of early‑life exposures may not be apparent until adolescence or adulthood; in certain cases, effects may also arise in later generations.

Behavioral Differences

Children often crawl, play close to the ground, and put hands and objects in their mouths, increasing the chances of ingesting pollutants in dust or soil (e.g., legacy contaminants such as lead; pesticide residues; or flame retardants in household dust). They also spend more time outdoors than most adults, which can increase the frequency of exposure to outdoor pollutants and hazards. 

The dietary needs of children and the means of acquiring nutrition also differ from those of adults (e.g., breast and bottle feeding), and children’s diets are often less varied. High consumption of certain foods (e.g., rice cereal, apple juice), can concentrate exposure to contaminants and pesticide residues that may be present. While human milk provides numerous benefits, certain pollutants can be present in breast milk and infant formula. Babies can also be exposed to substances their mothers encounter via the placenta during pregnancy. 

Because children rely on adults to create and maintain safe environments, actions like testing drinking water quality, reducing indoor air pollutants, and keeping play areas clear of environmental hazards are especially important.

Vulnerabilities by Childhood Lifestage

Children’s environmental health reflects exposures during early life, beginning with parental reproductive health and continuing through infancy, early childhood and adolescence to adulthood. 

Childhood comprises a series of life stages with distinct developmental periods, each with different risks and needs.  At each stage, biology and behavior shape susceptibility and exposure patterns in different ways. 

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Core Childhood Lifestages

From parental reproductive health through infancy, early childhood and adolescence, rapid changes in biology and behavior shape exposure and sensitivity.  

• Unique physiology refers to stage-specific traits (e.g., rapid growth and brain development, higher breathing and drinking rates per body weight, differences in skin absorption, metabolism, and changes in immune and hormonal systems). 
• Unique behaviors are the typical activities and settings at each stage (e.g., hand-to-mouth exploration, floor play and crawling, outdoor play and sports, increasing independence in product choices, and, for older teens, work conditions). 

The sections below describe each lifestage – age range, key physiology and behaviors, and common exposure examples – to help families, caregivers, educators, and community partners reduce risks where children live, learn, play and work.

Preconception: Parental Reproductive Health (People of Reproductive Age)

Children’s environmental health begins with parental reproductive health.

Unique Physiology

Some chemicals can remain in the body (e.g., lead) and be transferred to a developing fetus during pregnancy or to infants through breast milk. Because critical fetal development begins early, often before pregnancy is recognized, preconception exposures matter. Certain exposures can also affect partners and men, including impacts on sperm quality, fertility, and pregnancy outcomes.

Unique Behavior

Because early pregnancy is often unrecognized, people of reproductive age should reduce exposures before conception. Practical steps include maintaining a smoke-free home; using safer cleaning techniques and pest control; choosing simpler, fragrance-free products; testing drinking water quality and making plumbing-safe repairs (e.g., addressing lead and other contaminants as needed); and following local fish advisories.

Partners and men can also reduce exposures before pregnancy by avoiding tobacco and vaping and high heat exposures (e.g., hot tubs, saunas); limiting contact with lead, solvents, and pesticides; and preventing take-home dust and residues that can carry chemicals (e.g., changing clothes and shoes before leaving work, showering if possible, and washing work clothes separately).

Environmental Exposure Examples

Lead absorbed earlier in life can be stored in bones and later released during pregnancy or breastfeeding, exposing the fetus or nursing infant. Other chemicals — such as certain persistent organic pollutants — may accumulate in body fat and can similarly transfer during pregnancy and breast milk.

Prenatal: Conception to Birth

Unique Physiology

During pregnancy, women often breathe, drink, and eat more. Hormonal and metabolic changes affect how the body absorbs, distributes and eliminates substances. The placenta helps protect the baby, but it is not a perfect barrier. Some substances – like alcohol, nicotine, certain medications, and environmental pollutants – can cross the placenta and reach the fetus.

Unique Behavior

Many pregnancies are not recognized in the first six weeks, which can lead to unintentional exposures during early fetal development. Everyday environments and choices can increase exposure.

Environmental Exposure Examples

Chemicals in smoke and certain solvents can reach the fetus. Examples include secondhand tobacco smoke, some workplace chemicals (e.g., solvents, pesticides), certain household products (e.g., paint strippers, strong degreasers), and fish high in mercury (e.g., shark, swordfish, king mackerel). Exposures during pregnancy have been linked to higher risks of miscarriage, preterm birth, low birth weight, and some birth defects. Depending on the level and timing of exposure, substances such as secondhand tobacco smoke, certain solvents and pesticides, and methylmercury in some fish can reach the fetus. 

Infancy: 0 - 12 Months

Unique Physiology

During infancy, organs and defenses are still maturing. Infants undergo rapid growth and brain development, have increasing body fat, have more permeable skin, and higher breathing rates relative to their body weight. They also rely on breast milk or formula as the primary source of nutrition.

Unique Behavior

Infants engage in hand-to-mouth and object-to-mouth activities. They spend extended time sitting and crawling on the floor or ground and may start childcare or early care and education.

Environmental Exposure Examples

Children – especially those who are formula-fed – drink more water relative to their body weight than adults, which can increase exposure to contaminants in drinking water. Infants also breathe more air per body weight than adults, and indoor sources such as combustion byproducts from cooking or heating, volatile organic compounds from some products, mold, and resuspended dust can be important contributors to exposure.

Toddlerhood: 1 - 3 Years

Unique Physiology

During toddlerhood, organ system continues to mature amid rapid growth. The liver's enzyme activity peaks, helping kids effectively metabolize nutrients and medications and supporting growth, as well as defenses against environmental pollutants and infections.

Unique Behavior

Toddlers begin walking and exploration, spending significant time close to the ground, and frequently engaging in frequent hand-to-mouth and object-to-mouth activities. They also increase self-feeding and often attend childcare or early care and education.

Environmental Exposure Examples

A toddler may accidentally ingest lead through deteriorating lead-based paint and household dust in homes built before 1978, which can seriously harm their developing brain and nervous system. Frequent hand‑to‑mouth activity and proximity to floors and soil can increase ingestion of contaminated dust and soil; toddlers may also contact pesticide residues on floors and surfaces or ingest soil containing traffic‑related pollutants. 

Early Childhood: 3 - 6 Years

Unique Physiology

During early childhood, organ systems continue to mature with steady gains in, height and weight, rapid bone and skeletal growth, and developing muscle development and coordination. Children still breathe more air per body weight than adults, and their immune and respiratory systems are continuing to develop. 

Unique Behavior

Hand-to-mouth activity persists during play and meals, though less than in toddlerhood. Children engage in more vigorous play and exploration, and spend more time outdoors on soil, grass, and playground surfaces. They also may start preschool or school, and many attend childcare or early care and education.

Environmental Exposure Examples

As children spend more time outdoors, they may encounter outdoor-related hazards (e.g., pesticides on lawns and fields, contaminated soil and dust, heat and UV, ozone and wildfire smoke), depending on where they live and play. Indoor sources (e.g., cleaning and fragranced products, combustion byproducts, moisture and mold, and resuspended household dust) remain important contributors to exposure.

Middle Childhood: 6 - 11 Years

Unique Physiology

During middle childhood, children undergo rapid skeletal growth and bone mineralization, the reproductive organs begin to mature, and early puberty changes may emerge.

Unique Behavior

Children spend much of the day at school and in after-school programs. They also increase food consumption, relying on school meals and tap water.

Environmental Exposure Examples

Children in middle childhood spend much of their day indoors, especially at school. Inadequate ventilation and filtration, moisture and mold, contaminants in drinking water (e.g., disinfection byproducts or copper), and the use or misuse of strong cleaning or pest control chemicals can impair breathing and hinder learning.

Early Adolescence: 11 - 16 Years

Unique Physiology

During early adolescence, teens experience rapid bone growth, rising sex hormone levels, continued maturation of the reproductive system, and ongoing neurological development.

Unique Behavior

Adolescents have higher energy needs, resulting in more frequent snacking, larger portions, and greater participation in sports and outdoor activities. They also exercise greater independence in product choices and may begin employment.

Environmental Exposure Examples

With puberty and rapid growth, adolescents may be more sensitive to endocrine-active (hormone-active) chemicals. As food intake and independence increase, diet and food packaging can become important exposure sources, alongside personal care products and vaping and tobacco smoke.

Late Adolescence: 16 - 21 Years

Unique Physiology

During late adolescence, growth plates complete closure, sex hormone levels reach adult patterns (reproductive maturity typically achieved), and neurological development continues, with some regions still developing.

Unique Behavior

Adolescents have high caloric needs, increasing food intake. They engage in increased risk-taking behaviors and have expanded employment opportunities.

Environmental Exposure Examples

Older adolescents may encounter workplace exposures, such as cooking fumes and high heat in kitchens, dust and vehicle exhaust in warehouses, or strong cleaning and disinfecting chemicals, that increase the risk of breathing problems, skin and eye irritation, and heat illness while their bodies are still maturing. Exposure to vaping, tobacco smoke, and secondhand smoke is also linked to poorer lung and heart health. Some pollutants (e.g., certain solvents and some metals) can affect fertility and may influence future pregnancies.

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Childhood Development by the Numbers

During childhood, different body systems go through critical windows of development at different times, beginning in early pregnancy and continuing through childhood and adolescence. These windows underscore that the timing of exposure to pollutants is critical in protecting human health. Because different organs and systems develop on different timelines, early life exposures can have health consequences that may not become apparent until later in life; some effects may also arise in later generations.

• Skeleton: 1–12 weeks (prenatal)
• Heart: 3 – 8 weeks (prenatal)
• Major congenital anomalies: 3 – 32 weeks (prenatal)
• Lungs: 3 weeks – 10 years (postnatal)
• Central nervous system: 3 weeks – 20 years (postnatal)
• Reproductive system: 7 weeks – 20 years (postnatal)
• Immune system: 8 weeks – 10 years (postnatal)

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Protecting Children Now Creates a Healthy Future

Rates of chronic childhood health conditions are on the rise. More than 40% of school-aged children and adolescents live with at least one chronic health condition – such as asthma, obesity, and other physical or behavioral conditions –many of which last into adulthood (The MAHA Report - The White House).

Environmental factors – such as poor air or water quality – can cause or worsen these conditions, making it essential to highlight early lifestages when designing prevention strategies.

Improving children’s health creates ripple effects across the life course and generations, helping to: 

• Ensure healthy children grow into healthy adults.
• Enable healthy adults to build healthier families and communities.
• Foster better health across generations, supporting a more resilient society.

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Resources

EPA Resources

• Children’s Health Risk Assessment Tools and Guidance 
• Policy on Children’s Health 
• Exposure Assessment Tools by Lifestages and Populations – Lifestages
• Guidance on Selecting Age Groups for Monitoring and Assessing Childhood Exposures to Environmental Contaminants 

Other Federal Resources

• Managing Chronic Health Conditions in Schools (CDC)