8.2: Impacts from Natural Determinants of Health

Environmental health is concerned with preventing disease, death, and disability by reducing exposure to adverse environmental conditions and promoting behavioral change.

It focuses on the direct and indirect causes of disease and injury, both natural and anthropogenic, and taps resources within and outside public health and health care systems to improve health outcomes.

The natural environment impacts human health in many ways, but some of the most impactful and long-lasting effects stem from determinants rooted in unjust policies and socioeconomic systems (Table 1).

Table 1. Typical Environmental Health Issues: Determinants and Health Consequences.

How Society Affects Your Health

Society does a lot to improve our health, from sanitation to healthy foods. But society can also have negative effects on our health, and whether we experience positive or negative effects often depends on our social and economic standing.

Poverty, Health, and Environment

Global Health

Disease doesn’t care about national borders. The pathogen hopping the red eye from Berlin to Boston doesn’t need a passport. To be proactive in protecting our health, we need to think globally.

Environmental health risks can be grouped into two broad categories:

• Traditional hazards are associated with poverty and underdevelopment and primarily affect developing countries and those of lower socioeconomic status. These are most often women, children, those with disabilities/chronic illness, and other underrepresented minorities.
• Modern hazards, caused by technological development, prevail in industrialized countries where exposure to traditional hazards is low. In most developing countries, the contribution of modern environmental risks to the disease burden is similar to, and often greater than, that of developed countries. Urban air pollution, for example, is highest in parts of China, India, and some cities in Asia and Latin America.

Modern Hazards

Industrialized society releases vast amounts of pollutants and toxic waste into the biosphere, alters landscapes, and disrupts the global climate, resulting in a serious degradation of the Earth’s ecosystems. The consequences of such actions eventually impact human populations’ health and well-being.

• Air quality directly affects respiratory health, with exposure to pollutants such as ozone aggravating respiratory illnesses like asthma and COPD.
• Water quality is of paramount importance; contaminated water increases the risk of ingesting harmful chemicals, such as lead, and of contracting waterborne diseases.
• Food production and nutrition depend on the health of soil, water, and air.
• Food safety is also dependent on environmental health, as contamination during production, processing, and distribution can lead to outbreaks of foodborne illnesses such as salmonellosis.
• Waste management and sanitation systems are critical to protecting the environment and our health from contamination and diseases such as cholera.
• Climate change introduces another layer of complexity. More frequent extreme weather events, including extreme daytime and nighttime heat, significantly amplify risks. These events exacerbate respiratory and cardiovascular disorders and can lead to wildfires, which further degrade air quality. Warmer temperatures expand the range of disease-carrying vectors, thereby increasing the prevalence of vector-borne diseases such as Lyme disease, caused by Lyme borreliosis carried by ticks and transmitted directly to humans. Environmental disasters can impact our mental health, leading to disorders such as anxiety, PTSD, and depression.

Inequities compound these issues, with vulnerable populations disproportionately bearing the burden of environmental hazards, driven by factors such as proximity to industrial sites.

Chemical Agents

In terms of modern hazards, chemical agents have significant effects on human health.

Toxic heavy metals, dioxins, pesticides, and endocrine disrupters are examples of these chemical agents. Heavy metals (e.g., mercury, lead, cadmium) are typically produced as by-products of mining and manufacturing processes.

All of them biomagnify (become more concentrated as they move up the food chain). For example, mercury from polluted water can accumulate in swordfish to levels toxic to humans. When toxic heavy metals enter the body, they accumulate in tissues and may eventually cause illness or death.

Studies show that people with above-average lead levels in their bones have an increased risk of developing attention deficit disorder and aggressive behavior. Lead can also damage brain cells and affect muscular coordination.

Double-Burdens

In most areas of the world, the poor increasingly experience a “double burden” of traditional and modern environmental health risks. Their total burden of illness and death from all causes per million people is about twice that in rich countries, and the disease burden from environmental risks is 10 times greater.

The impact of traditional hazards exceeds that of modern health hazards by 10 times in Africa, 5 times in Asian countries (except for China), and 2.5 times in Latin America and the Middle East (Figure \(\PageIndex{1}\)). 

Figure \(\PageIndex{1}\). Traditional environmental health hazards prevail in developing countries, but modern risks are also significant.

Environmental Health, Women, and Children

Worldwide, the top killers of children under five are acute respiratory infections (from indoor air pollution); diarrheal diseases (mostly from poor water, sanitation, and hygiene); and infectious diseases such as malaria. Children are especially susceptible to environmental factors that put them at risk of developing illness early in life, and women who are pregnant or are of childbearing age are also at significant risk.

Double-Burdens

Around 2.1 billion people worldwide (around a quarter of the global population) cook using open fires or inefficient stoves fueled by kerosene, biomass (wood, animal dung, and crop waste), and coal, exposing people—mainly poor women and children—to high levels of indoor air pollution (IAP) (Figure \(\PageIndex{2}\)). 

Household air pollution was responsible for an estimated 2.9 million deaths per year in 2021, including over 309,000 deaths of children under the age of 5.& The combined effects of ambient air pollution and household air pollution are associated with 6.7 million premature deaths annually.

Household air pollution exposure leads to noncommunicable diseases, including stroke, ischaemic heart disease, chronic obstructive pulmonary disease (COPD), and lung cancer. Household air pollution accounted for an estimated 86 million healthy life years lost in 2019.  

Women and children, particularly in low- and middle-income countries, are typically responsible for household chores such as cooking and collecting firewood, and bear the greatest health burden from the use of polluting fuels and technologies in homes.

Adapted from: World Health Organization. (2025, December 16). Household air pollution. World Health Organization Fact Sheets. https://www.who.int/news-room/fact-s...ion-and-health

Figure \(\PageIndex{2}\). A girl cooking inside over an open-fire stove. P4173887 Rob Goodier/Engineering for Change, CC-BY-SA 2.0

Malnutrition

Malnutrition (the condition that occurs when the body does not get enough nutrients) is an important contributor to child mortality—malnutrition and environmental infections are inextricably linked. The World Health Organization (WHO) recently concluded that about 50% of the consequences of malnutrition are in fact caused by inadequate water and sanitation provision and poor hygienic practices.

Figure \(\PageIndex{3}\). Malnourished children in Niger, during the 2005 famine.

Poor Water and Sanitation Access

With 1.1 billion people lacking access to safe drinking water and 2.6 billion without adequate sanitation, the scale of these problems is significant. Each year, contaminated water and poor sanitation contribute to 5.4 billion cases of diarrhea worldwide and 1.6 million deaths, mostly among children under the age of five. Intestinal worms, which thrive in poor sanitary conditions, infect close to 90 percent of children in the developing world and, depending on the severity of the infection, may lead to malnutrition, anemia, or stunted growth. About 6 million people are blind from trachoma, a disease caused by the lack of clean water combined with poor hygiene practices.

Malaria

Malaria is an infectious disease spread by mosquitoes but caused by a single-celled parasite called Plasmodium, and one of the most impactful infectious diseases on Earth. Approximately 40% of the world’s people—mostly those living in the world’s poorest countries—are at risk from malaria. In 2024, there were an estimated 282 million cases and 610,000 deaths (mostly women and children), most in sub-Saharan Africa (most women and children). However, Asia, Latin America, the Middle East, and parts of Europe are also affected.

Pregnant women are especially at high risk of malaria. Pregnant women who are not immune to malaria risk both acute and severe clinical disease, resulting in up to 60% miscarriage and 10% maternal mortality. There is a 50% mortality rate for pregnant women with severe disease. Pregnant women who are semi-immune to malaria risk severe anemia and impaired fetal growth, even if they show no signs of acute clinical disease.

Malaria and the Environmental Consequences of DDT

Figure \(\PageIndex{4}\). DDT was a commonly used pesticide. This work OpenStax, CC-BY 4.0.

In addition to the diseases themselves, the measures to prevent them can sometimes also have environmental health consequences. For example, the insecticide DDT (dichlorodiphenyltrichloroethane) was widely used to control mosquito populations that transmit malaria in sub-tropical and tropical regions. However, after many years, the mosquitoes developed a natural resistance to DDT and again spread the disease widely. Anti-malarial medicines were also over-prescribed, which allowed the malaria pathogen to become drug-resistant.

The pesticide DDT was widely used for decades. It was seen as an ideal pesticide because it is inexpensive and breaks down slowly in the environment. Unfortunately, this characteristic allows the chemical agent to biomagnify through the food chain. Populations of top-predator bird species, such as eagles and pelicans, are severely affected by DDT. When these birds have sufficient levels of DDT, the shells of their eggs are so thin that they break, making reproduction impossible.

After DDT was banned in the United States in 1972, affected bird populations made noticeable recoveries, including the iconic bald eagle. DDT is still produced in the United States and transported to Central and South America, where it is used on many crops, some of which are imported back into the US.

The Impacts of Emerging Diseases

Emerging and re-emerging diseases are infectious diseases of humans whose occurrence during the past two decades has substantially increased or threatens to increase in the near future, relative to populations affected, geographic distribution, or the magnitude of impacts. Examples include COVID-19, Ebola virus, West Nile virus, Zika virus, severe acute respiratory syndrome (SARS), H1N1 influenza, swine and avian influenza (swine flu, bird flu), HIV, and a variety of other viral, bacterial, and protozoal diseases. Click here for an up-to-date global health map from Harvard: https://healthmap.org/en/

Emerging Disease or Emerging Diagnosis?

Toward the end of the 20th century, deadly microbes seemed to be springing up out of nowhere: Lassa virus in 1969, Ebola virus in 1976, and HIV in the 1980s. Public health officials classified them as "emerging diseases," meaning they are newly introduced or rising rapidly in human populations. Recent data, however, suggest these viruses may instead have been circulating widely for hundreds or thousands of years. We may not be contending with an emerging disease at all, but an emerging diagnosis of an ancient and frequent disease. This paradigm shift has implications for countering these viruses now before they become global threats.

A variety of environmental factors may contribute to the re-emergence of a particular disease, including temperature, moisture, and sources of human or animal food. Disease re-emergence may result from the coincidence of several environmental and/or social factors that create optimal conditions for disease transmission.

It seems likely that a wide variety of infectious diseases have affected human populations for thousands of years, emerging when the environmental, host, and agent conditions were favorable. Expanding human populations have increased the potential for transmission of infectious diseases due to close human proximity and the likelihood that humans will be in “the wrong place at the right time” for disease to occur (e.g., natural disasters or political conflicts). Global travel increases the potential for a carrier of disease to transmit infection thousands of miles away in just a few hours, as evidenced by WHO precautions concerning international travel and health.

Antibiotic Resistance

Antibiotics have been used for the past 80 years to treat patients with bacterial infections. Note: Antibiotics do not work to treat infections caused by viruses or fungi!

Since the 1940s, antibiotics have greatly reduced illness and death from these diseases and have been considered a miracle drug. However, for a number of factors, the infectious organisms the antibiotics are designed to kill have adapted to those medications, making the drugs less effective.

Antibiotic resistance occurs when bacteria change in ways that reduce the effectiveness of drugs, chemicals, or other agents designed to cure or prevent infections. This is caused by the process of evolution through natural selection (Figure \(\PageIndex{5}\)). Antibiotic-resistant bacteria survive and continue to multiply, causing further harm.

New forms of antibiotic resistance can cross international boundaries and spread between continents with ease. Many forms of resistance spread incredibly fast. Each year in the United States, at least 2 million people acquire serious infections caused by bacteria resistant to one or more antibiotics designed to treat them. At least 23,000 people die each year in the US as a direct result of these antibiotic-resistant infections. Many more die from other conditions that were complicated by an antibiotic-resistant infection. The use of antibiotics is the single most important factor driving antibiotic resistance worldwide.

Figure \(\PageIndex{5}\). Antibiotic resistance is a growing concern for medical professionals.

The Evolution of Bacteria on a "Mega-Plate"

Watch this famous experiment (the "Mega-Plate" experiment) conducted at Harvard Medical School, demonstrating that bacteria can adapt very quickly to conditions that should be deadly to them.

How Are Humans Responsible for Antibiotic Resistence?

Humans have largely caused the problem of antibiotic resistance through overuse and incorrect use:

• Individuals:
  • Self-prescribing antibiotics (available in many countries over the counter) or by pressuring a physician to prescribe them when an antibiotic is not needed. Antibiotics are among the most commonly prescribed drugs in human medicine, but up to 50% of those prescribed are unnecessary or not optimally effective.
  • Not taking the full course of a prescribed antibiotic (e.g., only taking 3 days of a 10-day prescription because you start to feel better).
• Healthcare workers:
  • Prescribing the wrong antibiotic for the type of bacterial infection.
  • Prescribing the improper dose for the infection.
• Society/Industry:
  • Wide use of antibiotics in the agricultural industry as a prophylaxis against infection. More than 50% of all antibiotics are given to livestock in the United States alone. Living and working near common livestock vector species is another frequent cause of antibiotic resistance. 
  • Poor infection control and sanitation. In recent years, there has been growing concern about a strain of Staphylococcus aureus that has become methicillin-resistant, known as MRSA. Another is VRSA (vancomycin-resistant Staphylococcus aureus). In the community, most MRSA infections involve the skin and may cause mild-to-moderate recurring infections in otherwise healthy people. Individuals who are immunocompromised or more susceptible may experience significant infections. For those who acquire MRSA in medical facilities (known as a nosocomial infection), MRSA can cause life-threatening bloodstream infections, pneumonia, and surgical site infections. Nosocomial infections are the leading cause of antibiotic-resistant illness. 
  • Fast global travel can spread infections quickly (also true for viral infections such as COVID-19, measles, and flu).
  • Reduced overall funding by governments and pharmaceutical companies for new antibiotic research.
  • Medications of poor quality with little regulatory oversight.

Additional Videos for Context

You are Mainly Microbe!

Ever not felt completely like yourself? There's a good reason for that. Because a large part of you . . . isn't you. Our bodies host ten times as many microbes as human cells. We are walking ecosystems, each of us home to thousands of different species on and inside of us. Meet your microbiome! Sure, some bacteria are dangerous, but without our tiny friends, we wouldn't be here (literally).

What Causes Antibiotic Resistance?

Explore how bacteria become resistant to antibiotics and turn into superbugs, and what scientists are doing to stop it.

How Can We Solve the Antibiotic Resistance Crisis?

Take a closer look at the challenges of antibiotic resistance and what we can do to prevent losing this vital medicine.

Suggested Supplementary Reading:

Koch, B.J. et al. 2017. Food-animal production and the spread of antibiotic resistance: the role of ecology. Frontiers in Ecology and the Environment (15)6: 309-318.

Notable Excerpts:

“Antibiotic use in food animals is correlated with antibiotic resistance among bacteria affecting human populations.” p. 311

“Microbial genes encoding antibiotic resistance have moved between the food-animal and human health sectors, resulting in illnesses that could not be treated by antibiotics.” p. 312