What Is Causing the Autism Epidemic?

What Is Autism?

Autism spectrum disorder (ASD) is a complex developmental disorder characterized by significant challenges in social interaction, communication, and behavior. The diagnosis is defined by the simultaneous presence in early childhood of symptoms in these three domains and has no established medical biomarkers. ASD has no single known cause, and there is considerable debate over the relative contributions of genetic and environmental factors. This debate has taken on increasing urgency as reported U.S. ASD rates have risen from 1-7 per 10,000 in children born before 1980¹ to 276 per 10,000 in children born in 2012.² In 2025, autism prevalence was reported as 1 in 31 children among children who were 8 years old in 2022. This sharp increase has fueled one of the most urgent debates in modern medicine: what is causing the autism epidemic.

Mainstream researchers often attribute the increase to changes in diagnostic criteria, better awareness, and expanded services. However, these explanations alone do not account for the staggering surge in prevalence, particularly over the past 30 years. Many parents and independent scientists argue that environmental triggers — including vaccines, their ingredients, and other toxic exposures — are key contributors, especially when combined with underlying genetic vulnerabilities.

The controversy over vaccines and autism erupted in the late 1990s, when more and more parents reported that their children regressed into autism following routine vaccinations. For many families, the regression was sudden and dramatic: loss of language, social connection, and developmental milestones in the days or weeks following immunization. These firsthand reports, coupled with research pointing to vaccine ingredients like thimerosal (a mercury-based preservative) and aluminum adjuvants, ignited a firestorm that continues today.

Government agencies and pharmaceutical companies have consistently denied a connection, citing cherry-picked and manipulated studies and high-profile court rulings. Yet large numbers of parental reports, scientific studies, and even compensated vaccine injury cases suggest that vaccines may play a significant role for some children. At the same time, other exposures — such as acetaminophen (Tylenol), pesticides, heavy metals, and endocrine-disrupting chemicals — have been implicated in increasing susceptibility to autism by weakening antioxidant defenses, altering brain development, and triggering chronic immune activation.

This clash between official narratives and independent evidence has made autism one of the most polarizing issues in public health. Families searching for answers are often caught between institutional denial and a growing body of research that demands deeper investigation into vaccines and environmental contributors to autism.

In November 2025, the CDC updated its website, to include a section titled “Autism and Vaccines.” Key points include:

• The claim “vaccines do not cause autism” is not an evidence-based claim because studies have not ruled out the possibility that infant vaccines cause autism.
• Studies supporting a link have been ignored by health authorities.
• HHS has launched a comprehensive assessment of the causes of autism, including investigations on plausible biologic mechanisms and potential causal links.

This shift represents a long-overdue break in the “case closed” narrative and an important opening for genuine, gold-standard science. For decades, CHD and countless families have called for transparent, independent research that does not start with the assumption that vaccines are exonerated. Acknowledging uncertainty, revisiting suppressed or ignored findings, and committing to a comprehensive review of biologically plausible mechanisms are essential first steps toward scientific integrity and justice for those harmed. CHD will continue to push for fully transparent data, independent replication, and policies that prioritize children’s health over protecting prior assumptions and institutional reputation.

The Controversy Over Vaccines and Autism

Many parents report that vaccine administration led directly to an observable autistic regression in their children.⁴ Due to the large number of vaccine injury claims filed for ASD under the National Vaccine Injury Compensation Program (NVICP), the claims were consolidated in 2002 under the Omnibus Autism Proceeding (OAP). The OAP was intended to try nine test cases covering three theories of injury, but only the six test cases for theories 2 and 3 went forward:

1. MMR vaccines alone caused autism
2. Thimerosal, the ethyl-mercury-containing preservative in vaccines, alone caused autism
3. MMR and thimerosal exposure in combination caused autism

In 2009, Special Masters of the United States Court of Federal Claims issued verdicts on the six test cases, rejecting each of these three theories and dismissing all of the OAP cases. Outside of the OAP, The NVICP has awarded compensation to numerous children who developed ASD after vaccination.⁵

Vaccine Ingredients

The OAP and the bulk of the published studies on vaccines and autism focus on one vaccine (MMR) and one ingredient (thimerosal). Beyond these specific theories, concerns have been raised about the expansion in the recommended childhood vaccines schedule, other vaccine ingredients such as aluminum adjuvants and the combined effect of multiple vaccines administered simultaneously.

Numerous reviews have examined environmental factors in autism risk. Many of these have found evidence suggesting that toxicant exposures, including mercury,⁶ may play a role in autism susceptibility. In addition, research highlighting the role of immune dysregulation and neuroinflammation in ASD⁷ suggests that the immunological responses elicited by vaccines and their ingredients merit further investigation, particularly in individuals with pre-existing metabolic or neuroimmune vulnerabilities.

Aluminum

Aluminum is the most common adjuvant used in childhood vaccines. Its purpose is to stimulate a stronger and longer-lasting immune response, but growing evidence suggests that this benefit may come at a significant neurological and immunological cost. Unlike dietary aluminum, which is only partially absorbed through the gut, injected aluminum bypasses natural barriers and can accumulate in the body. Studies show that aluminum particles can be carried by immune cells into the brain, where they may persist for years, activating microglia and fueling chronic inflammation — processes strongly implicated in autism spectrum disorder (ASD).^8-10

Epidemiological data reveal a troubling pattern: as the aluminum content of childhood vaccine schedules has increased, autism prevalence has risen in parallel. Animal studies confirm that even “vaccine-relevant” doses of injected aluminum can alter social behavior, impair motor function, and trigger long-term changes in brain development. Postmortem analyses of individuals with ASD have detected unusually high concentrations of aluminum in brain tissue, further supporting a biological link.

One of the best studies to exemplify the correlation between aluminum-adjuvanted vaccines and autism is a Danish study on 1.2 million children that showed statistically significant elevated risk in children who were exposed to aluminum adjuvants for several conditions, including autism. The authors (Andersson, et al.), however, refuse to acknowledge the results of their own study. Children’s Health Defense science team flushed out the statistical reasoning in a recent preprint (Jablonowski and Hooker). The study actually shows that children with aluminum exposure through vaccination were measurably and significantly more at risk for neurodevelopmental disorders, other pervasive developmental disorders, autistic disorder, autism spectrum disorder, and Asperger’s syndrome (now classified as level 1 ASD).

Defender articles:

• https://childrenshealthdefense.org/defender/study-claiming-no-link-between-aluminum-vaccines-autism-riddled-flaws/
• https://childrenshealthdefense.org/defender/aluminum-vaccines-autism-link-denmark-study-corrected-data/
• https://childrenshealthdefense.org/defender/journal-rejects-calls-retract-danish-study-no-link-aluminum-vaccines-autism/
• https://childrenshealthdefense.org/defender/new-peer-reviewed-analysis-casts-doubt-on-2002-study-claiming-no-link-mmr-vaccine-autism/

Polysorbate 80 / Polyethylene Glycol (PEG)

Polysorbate 80 and polyethylene glycol (PEG) are chemical additives (surfactants) commonly used in vaccines and other pharmaceutical products to stabilize ingredients and improve delivery. While often described as “inactive” or “safe,” these additives are biologically active compounds that can alter the way other substances move through the body. By design, they help shuttle nanoparticles and vaccine components across cellular membranes and protective barriers. This property raises concern when it comes to the delicate blood-brain barrier and developing gut lining in infants and young children.¹¹ In addition, PEG in particular has been associated with immediate hypersensitivity reactions, including anaphylaxis, in susceptible individuals.^12-13

Barrier effects

These surfactants can increase permeability of the gut and blood-brain barrier and aid nanoparticle transport.

Allergic risk

PEG is a well-documented trigger for immediate hypersensitivity in some individuals; caution is warranted in children with strong allergy histories.

Residual Human / Animal DNA & Proteins

Many vaccines are manufactured using human or animal cell lines, a process that can leave behind trace amounts of foreign DNA and proteins in the final product. While these fragments are considered “residual,” they are not biologically inert. Scientists have raised concerns that human fetal cell-line DNA, retroviral fragments, and animal proteins may interact with the immune system in unintended ways.^14-16 Potential risks include molecular mimicry, where the immune system confuses human proteins with foreign ones, sparking autoimmunity, and the possibility of DNA fragments integrating into the host genome, especially in rapidly developing cells of infants and young children.^14-16

Molecular mimicry and insertion risk

Trace human fetal cell-line DNA and retroviral fragments can persist in some biologics. Theoretical risks include immune cross-reactivity (autoimmunity) and genomic insertion events in susceptible individuals.^14-16

Temporal “change-point” correlations

Several ecological analyses reported autism prevalence change-points coinciding with introduction of certain human-cell-line–derived vaccines.¹⁴

Formaldehyde, Detergents, and Other Residuals

During vaccine production, a variety of chemicals are used to inactivate viruses, prevent contamination, or stabilize ingredients. These include substances like formaldehyde, detergents, and other manufacturing byproducts. Although present only in micro- to milligram amounts in the finished product, these residues are injected directly into the body, bypassing natural defenses like the digestive system. For most healthy adults, the body may quickly process and eliminate such exposures. But for infants and young children, especially those with immature detoxification systems or existing vulnerabilities, the combination of timing, route of exposure, and multiple co-exposures may magnify their impact on neurodevelopment and overall health.^17-18

Other Toxic Exposures

While vaccines and medications like acetaminophen are key concerns, they are not the only environmental factors linked to autism risk. Children today are exposed to a wide range of toxic chemicals in food, air, water, and household products, many of which have known effects on the brain, hormones and immune system. These exposures rarely occur in isolation; instead, they accumulate and interact, creating a “toxic load” that may overwhelm vulnerable children during critical windows of development. Pesticides, herbicides, flame retardants, heavy metals and air pollutants have all been associated with increased risk of neurodevelopmental disorders, including autism. The timing of exposure, especially during pregnancy and early childhood, appears to be a decisive factor in whether these chemicals disrupt healthy neurological growth.^19-22

Pesticides, Herbicides, and Industrial Chemicals

Glyphosate and PBDE flame retardants trend upward in exposure during the same era autism prevalence rose in many regions. Both are linked to endocrine disruption, neurotoxicity, and gut-immune dysregulation.^19-21

Air pollution and metals

Prenatal and early-life exposure to mercury, lead, and fine particulates correlates with increased autistic traits and adverse neurodevelopment in multiple cohorts.²²

Combined and Cumulative Exposures (“Stacking”)

Most research on vaccine safety looks at individual shots or single ingredients in isolation. But in real life, children are often exposed to multiple vaccines, adjuvants and medications at the same visit — all while living in environments filled with other toxicants. This practice of “stacking” exposures compresses immune activation into short windows and may overwhelm developing systems that rely on carefully balanced inflammation, detoxification, and repair.^23-25 For children with underlying vulnerabilities — such as mitochondrial dysfunction, methylation defects, or low glutathione reserves — the combined impact of vaccines, aluminum adjuvants, acetaminophen, and environmental chemicals can converge to produce neuroinflammatory cascades that set the stage for autism and related disorders.^23-25 Importantly, some studies suggest these effects are not the same for every child: boys and girls may respond differently, reflecting known sex-linked differences in immune regulation and detox pathways.

Same-day multiples

Simultaneous administration of several vaccines compresses immune activation into a narrow window, increasing fever and inflammatory signaling.^23-25

Multiple hits model

For children with mitochondrial, methylation, or detox vulnerabilities (e.g., low glutathione), stacked immune activations, aluminum adjuvants, and concurrent medications (like acetaminophen) may converge to produce neuroinflammatory cascades.^23-25

Sex differences

Some datasets show stronger effects in girls vs. boys — or vice versa — consistent with known sex-linked immune and detox differences.^23-25

Acetaminophen (Tylenol)

Acetaminophen is often recommended by pediatricians prior to and following vaccination appointments to reduce fever. For decades, parents have been told that Tylenol is the “safest” choice for managing childhood discomfort, and it has become one of the most widely used over-the-counter medications for infants and children. However, emerging research has raised serious concerns about the long-term neurodevelopmental impact of acetaminophen use, especially when given during critical windows of brain growth and immune activation, such as the newborn period, infancy and around vaccination.

Evidence has emerged over the past two decades pointing toward exposure of susceptible babies and children to acetaminophen as a factor leading to autism spectrum disorder (ASD). The scientific literature has supported the theory that neurodevelopmental risks from acetaminophen exposure are greatest during the peripartum period.²⁶

The first study probing the connection between acetaminophen use and ASD was published by Schultz in 2008.²⁷ That study suggested that the vast majority of all cases of regressive ASD might be attributable to acetaminophen exposure. A causal relationship has been inferred from a large and robust body of more recent evidence: Good, 2009; Good, 2018; Shaw, 2013; Patel et al., 2022; Zhao et al., 2023; Parker et al., 2023; Jones et al., 2024.

CHD scientists investigated the association between ASD and medical conditions that normally result in acetaminophen exposure during childhood.²⁸ Children had a 126% greater chance of developing ASD if they had at least one documented condition for which acetaminophen may be used, and a 163% greater chance if they had at least four such conditions.

Defender article:
https://childrenshealthdefense.org/defender/repeated-diagnosis-fever-pain-early-childhood-strong-association-autism-research-report-chd-science-team/

CHD TV “Doctors & scientists”:
https://live.childrenshealthdefense.org/chd-tv/shows/good-morning-chd/tylenol-concerns/

Preprint link:
https://www.preprints.org/manuscript/202509.1344/v1

Glutathione depletion

Acetaminophen is metabolized to a reactive intermediate (NAPQI) detoxified by glutathione (GSH). Infants have limited reserves; dosing around vaccine-induced fever can further deplete GSH, the body’s primary antioxidant, which is critical for brain development and heavy metals detox.

Epidemiology

Multiple analyses (prenatal and early-life exposure) report higher odds of autism traits or diagnosis with greater acetaminophen use. Large administrative-data studies using “exposure surrogates” (diagnoses likely treated with acetaminophen) have found dose-response patterns, with stronger signals in girls in some cohorts.

Mechanisms

Glutathione depletion → oxidative stress, microglial priming, and impaired endocannabinoid signaling — each implicated in ASD biology.

Immune Dysregulation and Neuroinflammation (Why Timing Matters)

One of the most consistent findings in autism research is evidence of immune system abnormalities and chronic neuroinflammation in affected children. Timing is critical: when the immune system is repeatedly activated during sensitive stages of brain development — such as infancy and early childhood — it can alter the way neurons connect, prune, and mature.^29-32 This dysregulation doesn’t occur in a vacuum. Children with underlying mitochondrial dysfunction, oxidative stress, or detox vulnerabilities are especially at risk, as their cells struggle to cope with repeated inflammatory signals.³¹ Meanwhile, disruptions in the gut–brain axis — driven by adjuvants, surfactants, or environmental toxicants — can further fuel systemic inflammation and microglial activation in the brain.^30-32 Together, these processes create a cycle of immune stress and neuroinflammation that is increasingly recognized as central to the biology of autism.

Cytokine surges in critical windows

Repetitive immune activation during rapid synaptogenesis can alter pruning, myelination, and neuronal connectivity.^29-32

Mitochondrial vulnerability

A notable subset of autistic children shows mitochondrial dysfunction; immune activators and toxins that stress mitochondria (e.g., thimerosal, acetaminophen via GSH depletion) can magnify injury.³¹

Gut–brain axis

Adjuvants and surfactants can shift gut permeability and microbiota; microbial products then reinforce systemic inflammation and microglial activation in the brain.^30-32

Vaccinated Children Vs. Unvaccinated Children

CHD published “Vax-Unvax: Let the Science Speak” in 2023, written by Brian Hooker, PhD and Robert F. Kennedy Jr.

“Vax-Unvax” compiles dozens of observational and administrative-data studies comparing fully/partially vaccinated children with those who are minimally or entirely unvaccinated. Across many datasets, the authors report higher rates of chronic illness in vaccinated cohorts—including autism and other neurodevelopmental diagnoses (ASD/ADHD/learning disorders), asthma and allergies (eczema, allergic rhinitis), recurrent ear infections and ENT surgeries, and gastrointestinal and autoimmune conditions, while vaccinated groups predictably show lower rates of several acute infections.

The authors argue that “schedule intensity” (more shots earlier, plus aluminum adjuvants and same-day multiples) and co-exposures (e.g., acetaminophen) correlate with worse long-term outcomes, especially in children with mitochondrial/immune vulnerabilities. The book critiques CDC-funded literature for design flaws and conflicts, highlights independent studies (including practice-based cohorts) that find elevated risk ratios for chronic conditions in vaccinated groups, and calls for large, fully independent, prospective vax-vs-unvax studies and transparent access to raw health-system data.

Here are a list of studies to support these findings:

Hooker and Miller 2020 (https://journals.sagepub.com/doi/10.1177/2050312120925344)

JLW and Blaylock 2022 (https://www.researchgate.net/publication/363882194_Revisiting_Excess_Diagnoses_of_Illnesses_and_Conditions_in_Children_Whose_Parents_Provided_Informed_Permission_to_Vaccinate_Them)

Hooker and Miller 2021 (https://www.oatext.com/pdf/JTS-7-459.pdf)

Mawson et al. 2025 (https://publichealthpolicyjournal.com/vaccination-and-neurodevelopmental-disorders-a-study-of-nine-year-old-children-enrolled-in-medicaid/)

Mawson et al. 2017 (https://www.oatext.com/pdf/JTS-3-186.pdf)

Garner, 2021 (https://ijvtpr.com/index.php/IJVTPR/article/view/40)

Summary

Despite repeated government efforts to dismiss concerns through the Omnibus Autism Proceeding and selective industry-funded studies, a substantial body of scientific evidence and thousands of consistent parental reports continue to implicate vaccines and their ingredients as significant drivers of the autism epidemic. Independent analyses have found strong associations between thimerosal exposure, aluminum adjuvants, and the expanding vaccine schedule with sharply rising rates of neurodevelopmental disorders. Beyond these ingredients, research also points to the compounding role of acetaminophen use, pesticide exposure, heavy metals and other toxicants, all of which can weaken antioxidant defenses, disrupt immune function, and impair healthy brain development.

With autism prevalence soaring from a once-rare condition to 1 in 31 children today, and studies identifying plausible biological mechanisms including mercury toxicity, glutathione depletion, oxidative stress, immune dysregulation, and chronic neuroinflammation, the evidence can no longer be ignored. The sharp rise cannot be explained by genetics or diagnostic changes alone. Instead, it reflects the convergence of multiple environmental triggers — vaccines chief among them — that overwhelm vulnerable children during critical windows of neurodevelopment.

The urgent task before us is accountability and transparency. Rather than suppressing, distorting, or dismissing this evidence, public health authorities must confront the possibility that medical practices and chemical exposures — once assumed safe — are fueling the autism crisis. Only by openly acknowledging and addressing these risks can we begin to reverse the epidemic and protect future generations.

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