Autism Spectrum Disorder (ASD) impacts a significant number of individuals globally. While genetics play a strong role, researchers have been increasingly exploring how environmental factors contribute to the risk of developing autism.
In recent years, compelling evidence has emerged linking pollution, chemicals, and even maternal health during pregnancy to neurodevelopmental outcomes in children. In this article, you will explore how the development of autism is linked to environmental factors.
1. The Genetic-Environmental Connection
Autism Spectrum Disorder is widely recognized as a neurodevelopmental condition with strong genetic roots. In fact, studies involving twins and families show that genetics can explain up to 80% of autism risk. However, genes alone don’t tell the whole story.
Gene-Environment Interaction
Think of our genes as a blueprint and the environment as the builder. A person may be genetically predisposed to autism, but it often takes specific environmental exposures or stressors at the right (or wrong) time to "activate" these underlying risks. This is called a gene-environment interaction.
Here’s how it works; A child may carry genetic variants that increase sensitivity to environmental factors. If that child is then exposed to certain pollutants, chemicals, or infections during critical stages of brain development, particularly in the womb or early infancy.
Those exposures can influence how those genes are expressed. This process, called epigenetics, doesn't change the DNA itself but alters how the genes behave like turning a dimmer switch up or down.
The brain develops rapidly during pregnancy and early childhood, which makes these periods highly sensitive to environmental influences. Exposures during this time can disrupt the formation of neural connections, alter the immune response, or affect hormone regulation. All of these aspects play a role in how autism traits develop.
A study published in Translational Psychiatry investigated early medical events and their association with Autism Spectrum Disorder in twins. The findings indicated that monozygotic (identical) twins, who share the same genetic makeup, can exhibit discordance for ASD.
This suggests that non-shared environmental factors, such as prenatal and perinatal complications, may contribute to the development of autism in one twin but not the other.
2. Air Pollution- A Growing Concern
A major new study published in Brain Medicine shows a strong association between air pollution and autism risk. It highlights a significant link between prenatal exposure to nitric oxide, a pollutant from vehicle emissions, and an increased risk of ASD in children.
The research suggests that Nitrogen Oxide (NO) exposure during pregnancy can disrupt normal brain development, especially in genetically predisposed individuals. Maternal inflammation caused by pollution may impact fetal brain development.
Also, prolonged neuroinflammation triggered by pollution may affect regions of the brain involved in social and cognitive functions- areas often affected in ASD.
Another research indicates that maternal exposure to higher concentrations of Nitrogen Dioxide (NO₂) before and during pregnancy is associated with greater odds of ASD in offspring. This underscores the importance of air quality during critical developmental windows.
3. Chemical Exposure During Pregnancy
In addition to air pollution, studies have identified several environmental chemicals that may play a role in autism risk:
Bisphenol A (BPA)
A decade-long study by the Florey Institute in Australia established a connection between prenatal exposure to BPA, a chemical found in plastics, and an increased risk of ASD in boys.
The study found that boys born to mothers with higher BPA levels during late pregnancy were significantly more likely to exhibit autism symptoms by age two and receive a diagnosis by age eleven.
Phthalates & BPA
Phthalates are used to soften plastics and are also found in things like shampoos, soaps, and fragrances. Whereas, BPA is used in making hard plastics, like those used in food containers and water bottles, and in the lining of canned foods.
They’re classified as endocrine-disrupting chemicals (EDCs), which means they can interfere with the body’s natural hormone system. Hormones play a big role in brain development, especially in the womb and early childhood.
When pregnant women are exposed to phthalates and BPA, these chemicals can mimic or block natural hormones, like estrogen and testosterone. This hormonal disruption can impact how the baby’s brain develops in utero, potentially affecting behavior, learning, and emotional regulation later in life.
Heavy Metals (like mercury and lead)
These metals are neurotoxic. They can interfere with the way the brain and nervous system develop. This is especially critical during pregnancy when the baby's brain is forming its most important structures.
If a developing fetus is exposed to mercury or lead, even in low amounts, it can disrupt the wiring of the brain, affect how neurons grow and connect, and increase the risk of developmental delays and behavioral challenges.
Lead exposure remains a significant concern in older homes (through old paint and plumbing), contaminated soil, and some imported products. It doesn’t take much lead to pose a risk even low levels in the bloodstream have been associated with lower IQ, attention difficulties, and learning problems.
Organophosphate pesticides
A large-scale study from UC Davis’s MIND Institute found that children born to mothers exposed to organophosphate pesticides during pregnancy had a 60% higher risk of developing autism. The study analyzed data from over 1,000 participants in the Northern California-based Childhood Autism Risks from Genetics and the Environment (CHARGE) Study.
By linking California's commercial pesticide use records to the residential addresses of pregnant women, researchers observed that approximately one-third of the study participants lived within a mile of pesticide application sites during their pregnancies.
4. Maternal Health & Prenatal Environment
Environmental factors also include the health and conditions experienced by the mother during pregnancy. These include:
- Maternal infections and fever
- Gestational diabetes
- Obesity or malnutrition
- Stress and anxiety
Such conditions can lead to immune activation or inflammation that alters fetal brain development. For example, high levels of maternal cytokines (immune proteins) have been associated with impaired social behavior in offspring.
5. Environmental Inequities- A Public Health Issue
Children living in low-income or marginalized communities often face higher environmental exposure risks i.e., from poor air quality to substandard housing with mold or lead. This highlights a pressing need for:
- Equal access to clean air and water
- Regulation of pollutants
- Targeted healthcare support in at-risk areas
What You Can Do?
While some factors are beyond individual control, there are steps expecting families can take:
- Avoid areas with high air pollution if possible.
- Use non-toxic personal care products.
- Eat a nutrient-rich, balanced diet.
- Avoid exposure to pesticides and plastic containers with BPA.
Conclusion
It’s important to note that no single environmental factor causes autism. Rather, it’s a complex mix of genetic sensitivity and environmental triggers that may shape how autism develops. Understanding the link between autism and environmental factors empowers families and communities to make informed decisions and push for healthier environments.
While we can’t change our genes, we can improve the world we live in and every cleaner breath, safer product, and informed policy can contribute to healthier outcomes for future generations.
Note: This article does not contain any behavior analytic content.