This may be no more than a conspiracy theory at this point, because there's no causal link between the two. But it struck me that increases in autism and ADHD are coincident with the increase in plastics in the environment. Here's what I found.
There is currently no direct causal evidence proving that microplastics cause autism or ADHD in humans, though emerging animal and observational studies suggest that plastic particles and associated chemical additives may act as environmental risk factors. Scientific focus has been on chemical plasticizers and additives that leach from plastics rather than the solid plastic particles themselves.
"Studies on exposure to microplastics indicate an increase in oxidative stress and inflammation as well as a decline in attention and memory...no evidence [yet] for a causal relationship between microplastic particles and ASD [though it may be an] environmental factor influencing neurodevelopment" ref
Nanoplastics can cross biological barriers—including the blood-brain barrier—potentially inducing oxidative stress and neuroinflammation.
Mouse models show prenatal exposure to synthetic plastics like polyethylene can trigger gut microbiome shifts, brain metabolite changes, and autism-like behavioral traits.
Children with ASD or ADHD often show reduced efficiency in detoxifying common plastic chemicals like bisphenol A (BPA) and di(2-ethylhexyl) phthalate (DEHP) through a liver clearance process called glucuronidation. ref
Observational human studies (such as infant cohort analyses) have linked prenatal exposure to plasticizers like DEHP or BPA with higher rates of autism- and ADHD-related traits or altered epigenetic markers (DNA methylation) in early childhood.
Is the timing of the rise in ADHD and autism closely correlate in the rise of plastic production and use around the world?
Proponents of this view argue that the parallel timeline isn't a coincidence. The sheer volume of global plastic production means that children born over the last 25 years have experienced unprecedented, continuous, in-utero and early-life exposure to microplastics and leached endocrine-disrupting chemicals (like BPA, phthalates, and DEHP). Because these chemicals actively disrupt fetal neurodevelopment and hormone pathways, the massive surge in plastic production is viewed as a highly probable environmental driver fueling a genuine increase in these conditions. ref
However, a confiunding factor here is the broader definition and recognition of these disorders within the same timeframe as the rise of plastics.
The medical definitions of both autism and ADHD were fundamentally rewritten during this timeline, most notably in 1994. Conditions like Asperger’s and milder sensory or behavioral traits were folded under the broader "Autism Spectrum Disorder" umbrella, instantly capturing millions of children who wouldn’t have qualified for a diagnosis in the 1970s. Decades ago, mild or moderate neurodivergence went entirely unnoticed or unlabeled.
