Global mean temperatures are rising around the world in part because of human activity (1). Record-setting heat waves are occurring with greater frequency and lasting longer than ever before (2) (Figure 1). The past decade (2015–2024) has been the 10 warmest years on record, with 2024 being the hottest year on record (3). Although policies and global actions have attempted to lower emissions from the burning of fossil fuels to meet the goals of the Paris Accord (limit global temperature rise to 2°C above preindustrial levels by the end of the century and to pursue efforts to hinder temperature increase to below 1.5°C), it is unlikely that this will be met due to inadequate political commitment (4). Exposure to extreme heat is known to put strain on numerous biological systems, which contributes to increased morbidity and mortality, particularly among older individuals and those with heart and lung conditions, and it is thus critical that we take steps to address the potential public health burden of increasing extreme heat.

However, while the health effects of extreme heat are well known, there has been little discussion on the unique impacts of heat on early childhood development. Early development is associated with rapid development across biological systems that support long-term behavioral, physical, and emotional health into adulthood. Indeed, emerging evidence suggests that extreme heat exposure is associated with low birth weight and prematurity, learning loss during the school years, and heat-related illness with life course health implications (5). Given extreme heat puts a strain on key developing systems, understanding the potential impact during early childhood and identifying solutions for ameliorating potential harm, is necessary to advance public health. Here, we offer our perspective and argue for increased attention to, and support for, the impacts of extreme heat on the developing child in the United States. We first highlight extant literature on the biological effects of heat on young children. We further discuss potential solutions that consider the unique developmental needs of children to support them against the adverse effects of extreme heat.

Increasing temperatures and heat are likely to impact every region on earth and similarly can affect every organ and cell in the body. Extreme heat refers to when temperatures are significantly higher than normal for any given location. In the brain, extreme heat can lead to slowed cognition and disruptions in emotional functioning—particularly attention, memory, and information processing (6). In the gut, high temperatures can cause the gut lining to become “leaky,” allowing bacteria to penetrate the intestinal barrier and enter the bloodstream (7). During longer periods of exposure, these biological changes can increase the risk of harmful bacteria and toxins reaching the body’s vital organs via the circulatory system. This “invasion,” in turn, further activates the immune system leading to systemic inflammation (8). Heat exposure also increases blood flow to the skin while decreasing its flow to the muscles and other organs, which may cause muscle tissue damage and release proteins into the bloodstream that can cause arrhythmia, kidney damage, and seizures (9). Cells produce heat shock proteins, which act as “chaperones” that stabilize the structure of other proteins that high temperatures could damage. Over short periods of time, heat shock proteins are effective and helpful, but when temperatures are high for too long, they lose their ability to function, and the proteins they protect start to break down (10). This can have a variety of long-term impacts on health, including activation and misdirection of the immune system against proteins that have broken down, leading to increased susceptibility to infections and a decreased response to vaccines (11).

In the prenatal period, heat may result in reduced blood flow in the placenta, dehydration, and inflammation, all of which can trigger preterm birth (12), increase rates of stillbirth (13, 14), or lead to babies born with lower birth weight, all of which are linked to greater risk of a range of poor outcomes later in life including mortality. Additionally, exposure to extreme heat in the first trimester of pregnancy may increase the risk of some birth defects (15). The consequences of being born too early or too small include an increased risk of impaired cognition, reduced growth, and chronic health issues such as cardiovascular disease and diabetes in adulthood (16–22).

During early childhood, biological systems are rapidly developing, making them especially sensitive to exposures from the environment. While heat affects individuals of all ages, the fetus, infant, and young child are more sensitive to heat exposure than most older children and adults, because their smaller bodies heat up more quickly, and they have less capacity to release heat via sweating (23–25). The biological systems that regulate body temperature in infants and young children are less developed and less efficient (26). Infants and young children also rely on adults to seek out cooler environments or get water to drink (24, 25).

Exposure to extreme heat in children has been associated with lower cognitive function, reduced ability to concentrate, decreased sleep quality, and adverse outcomes in mental and behavioral health. One analysis of school-age children in the US and Europe calculated that the temperature for optimal concentration is 72°F (22°C) or lower. Student performance on psychological tests and school tasks can be expected to increase on average by 20% if classroom temperatures are lowered from 86°F to 68°F (30–20°C) (27). Conversely, studies show that school performance decreases as temperatures rise. In New York City, for example, learning losses increased by up to 50% when school-day temperatures went above 100°F compared to days above 90°F. In addition, the learning loss from extreme heat events can be lasting: Hotter school days two, three, and even 4 years prior to a test correlate to lower scores (28).

Temperature plays an integral role in sleep quality. During the 2022 heat wave in the UK, researchers studied the impact of high temperatures on infants’ sleep. They found that when temperatures ranged from 96°F to 102°F, infants took longer to fall asleep, had less total sleep, had less efficient sleep, and had more fragmented sleep, and parents’ visits were more frequent during the night. Sleep deficits in infancy increase the likelihood of experiencing emotional and behavioral challenges in early childhood, disrupted language development, and reduced problem-solving skills (29, 30).

The brain detects extreme heat as a threat to wellbeing, which activates the stress response system (31, 32). Excessive activation of the stress response system during pregnancy and in early childhood can disrupt the development of healthy emotional regulation circuits in the developing brain of a child or fetus (33). Excessive heat has been shown to increase violent crime, conflict, and suicide due to a combination of biological and environmental factors (34–36). Experiences of violence are potent activators of the stress response during pregnancy and in young children and can cause long-lasting trauma, decrease a sense of physical and psychological safety and contribute to the development of mental and behavioral health problems in children (37–40).

All children face risks from extreme heat, but these risks and their impacts are not evenly distributed and disproportionately affect those in lower socioeconomic groups. The impact of heat is greatest in low-income communities of color (41), where decades of discriminatory zoning and redlining led to the creation of urban heat islands dominated by heat-trapping asphalt, densely concentrated buildings, traffic, industry, and highways (26, 42, 43). Multiple studies show that nearly all US neighborhoods that were subject to redlining are hotter today than non-redlined neighborhoods (42) and have higher levels of air pollution (44). These neighborhoods also tend to have less access to ways of reducing children’s exposure to excessive heat due to systematic underinvestment in infrastructure. For example, lower-income students are more likely to be in schools without adequate air conditioning than higher-income students, and Hispanic and Black households are less likely to have access to air conditioning compared to white households (45). Rural areas are not immune to inequities: More than half of rural US counties have no hospital obstetric services, and the odds of having no local health services for pregnancy and delivery are greatest in lower-income rural counties with more Black women of reproductive age (46). Having to travel long distances to obstetric care for heat-related pregnancy complications likely contributes to higher rates of maternal death, infant death, and childbirth challenges in rural areas (47). This type of documented inequity offers guidance for prioritizing heat-reducing measures where they will have the highest impact on those with the greatest need.

In addition to economic status and geographical location (urban vs. rural), other factors such as diet, living conditions, and stage of development shape the impact that heat has on a child’s health and development. Extreme weather events associated with climate change also impact child health. For examples, wildfires worsen air quality and poorer air quality cause more children to develop asthma and, among children with asthma, exacerbations (48). Extreme heat leads to drought and affects plant and animal health, which impacts the food supply and lowers access to nutritious foods. It also can lead to reduced breast milk production, decreased appetite, and increased burden of infectious diseases such as diarrhea that diminishes an infant’s ability to absorb nutrients, all of which can lead to stunting (49, 50). Therefore, exposure to extreme heat cannot be addressed alone without considering how the conditions in which young children live affect the way that they experience extreme heat.

Long-term solutions require us to decrease our dependence on fossil fuels and lower greenhouse gas emissions, which will have a positive effect across multiple domains of children’s health. Practical solutions are being implemented in many parts of the world to mitigate and, separately, adapt to climate change. Mitigation strategies include a wide range of policies and private- sector actions that facilitate a shift from fossil fuels to renewable energy sources, increase energy efficiency and boost natural carbon sequestration. Adaptation strategies include improved access to clean water and food supplies, protection against extreme weather events, availability of cooling technologies, and addressing long-standing inequities that are the root cause of health disparities. Strategies that address high temperatures and other aspects of climate change are also strategies that promote the healthy development of children. Further, studies show that policies that target emissions, for instance, can both benefit children’s health and save on health costs. As just one example, the Regional Greenhouse Gas Initiative—a cooperative effort among 12 states in the northeastern United States to reduce carbon dioxide emissions from power plants—is estimated to have prevented more than 16,000 cases of respiratory illness, 537 new cases of asthma, and other illnesses in children, with substantial savings in health care costs in 5 years (51).

However, there are actions we can take today that can have immediate benefit. Federal agencies must continue to prioritize climate research - to better understand health impacts, to guide policy, and help us be more prepared. A strong Environmental Protection Agency is needed to protect both planetary and human health. A range of practical strategies and approaches to address the effects of excessive heat on children are already demonstrating positive impact in the world (see Table 1). Below we highlight a few examples.

The increasing severity and frequency of heat waves will increase the risk of acute and long-term health effects. Fetuses, infants, and young children are more sensitive to the effects of these heat waves as their bodies are still developing and their thermoregulatory capacities are limited. While global temperatures are expected to increase, the extent of these increases will depend on human actions to mitigate greenhouse gases. It is therefore critical that while action is taken via use of early monitoring systems and redesigning our local environments to reduce heat exposure, it is also critical that there is collective action to mitigate global warming by reducing greenhouse gases. Local, state, national, and international agencies must work together to advance meaningful change for the future of children across the globe.