Americans living in the Midwest are most likely to have a toxin linked to autism hidden in their homes, a study suggests.

Researchers combed through census data for 500 cities to calculate the number of homes that still contain lead paint, which was banned in the 1970s for its links to developmental delays and behavior issues in children.

And recent research suggests lead exposure could be tied to rising autism cases across America. 

But even in 2025, roughly 38million homes throughout the country – one in four – were built prior to the ban and may still contain the paint on windowsills, doorframes, stairs, railings, porches and fences. 

After calculating a score out of 100, with higher scores signaling greater risk based on when houses in the area were built, researchers behind the new study found people living in St Louis, Missouri, are the most at risk of living in a lead-filled home, earning a score of 65. 

Nearly 60 percent of houses in the city were built before 1939, when the vast majority of houses used lead in their construction. 

And one in 10 homes in St Louis were built between 1960 and 1979, the end of the lead paint era. 

Meanwhile, just across the Mississippi River, Chicago had the second-highest lead exposure risk, scoring 52 out of 100. 

A new study has ranked the cities most at risk of having lead paint in homes, which has been tied to autism (stock image)

About 40 percent of homes – 500,000 – in the Windy City were built before 1940, and just four percent were built after 2010.  

However, the researchers noted Chicago has more continuous growth than St Louis, meaning it has more new builds and increased renovations – meaning lead paint is more likely to be replaced. 

Kansas City, Missouri, was the third-worst city in the study, scoring 50 out of 100. The city’s health department estimates 84,000 homes in the area were built before the lead paint ban and only around 1,500 have had it removed. 

Cicero, Illinois, just outside of Chicago, and Philadelphia rounded out the top five most lead-ridden cities, each scoring about 49.6 out of 100. 

Meanwhile, three cities in Arizona – Gilbert, Surprise and Goodyear – along with Johns Creek, Georgia, and Frisco, Texas, had the lowest risk of lead exposure, all scoring around 29 out of 100 points. 

In Arizona, just two percent of homes were built before 1939, which could contribute to them being less likely to have lead. And in Frisco, just under one percent of home fit this criteria. 

The report, from Home Gnome, comes as health secretary Robert F Kennedy Jr has announced a series of studies looking into ‘environmental toxins’ he believes could be behind a rise in autism in the US.  

The latest data shows one in 31 children in the US are thought to have autism, a staggering increase from about one in 150 in the early 2000s.

Lead paint that is well maintained is generally safe, but when it peels, it releases dust and paint chips that children may ingest. 

Dr Ryan Sultan, psychiatrist and research and medical director at Integrative Psych in New York City, told the Daily Mail: ‘Exposure to lead has long been associated with neuro developmental conditions, including autism and ADHD. Most often medicine believes the association to be driven by children eating paint chips.

‘Lead paint has not been used in many years. However, the cities cited in the study are older cities with homes that have many layers of paint on them— earlier layers of paint likely contain lead.’ 

There is no safe level of lead exposure, according to the CDC, as it has been shown to attack the kidneys, reproductive, cardiovascular and digestive systems. 

It’s also been linked to IQ loss and developmental delays, as well as autism. It’s thought to interfere with communication between brain cells, particularly in areas responsible for learning.

It may also cause inflammation and reduce overall brain volume, shrinking structures like the prefrontal cortex, which is responsible for decision-making, impulse control and reasoning.  

Dr Kimberly Idoko, neurologist and medical director at EverWell Neuro, told the Daily Mail: ‘Lead doesn’t directly cause autism, but it can raise the risk in children who are biologically susceptible by interacting with genetic and other environmental factors.’

This includes children with certain gene mutations and whose mothers had high-risk pregnancies. 

‘Lead is a neurotoxin that disrupts synapse formation, myelination, and neurotransmitter function, especially during pregnancy and early childhood when the brain is most vulnerable,’ Dr Idoko explained. 

‘And it drives oxidative stress and neuroinflammation, which are increasingly implicated in neurodevelopmental disorders like autism.’

A 2022 study in the journal Pediatric Research found autistic children had 43 percent higher levels of lead in their blood than neurotypical children. 

And another 2022 meta-analysis of 61 studies found 47 percent higher lead in the hair of autistic individuals than neurotypical controls.

This can lead to exposure decades after the paint was originally outlawed. A 2021 study in JAMA Pediatrics, for example, found of 1.1million US children under six, half had detectable levels of lead in their blood. 

Pictured above is a row of homes along Lafayette Square in downtown St Louis. The city of 280,000 was most at risk of lead paint exposure in homes, according to the new report

Gilbert, Arizona (pictured here), meanwhile, had the lowest exposure risk, despite being roughly the same size as St Louis. This could be due to a larger number of newly built homes

In St Louis, a city of 280,000, 58 percent of homes were built before 1939. During this time, roughly 87 percent of homes used lead paint.

Additionally, about 17 percent were built between 1940 and 1950 and 10 percent were built between 1960 and 1979. Lead paint wasn’t banned in US residential construction until 1978. 

St Louis offers free lead inspections for residential properties where pregnant women or children under six live. If lead is found, the family may qualify for financial assistance to remove it, but it depends on household income. 

However, a May report from St Louis Magazine found money that was meant to be saved for the city to remove lead from properties was allocated elsewhere. 

Last year, the Environmental Protection Agency (EPA) announced $44million from the Biden administration would be dedicated to helping Missouri remove its lead pipes. 

The EPA also collected $65,000 collectively in penalties from eight St Louis home renovation companies who had violated the Toxic Substances Control Act, which is meant to reduce lead-based paint hazards during renovations.

The above map from Natural Resources Defense Council (NRDC) shows populations served by drinking water with the highest levels of lead contamination. Florida had the highest concentration of lead piping, a separate study showed

Chicago was the second-most at-risk city for lead exposure, scoring 52 out of 100 possible points.  

The Home Gnome researchers did not provide exact figures, but another recent study from Filter Buy found 40 percent of homes were built before 1940, which adds up to 492,000. Meanwhile, just four percent were built after 2010.

The Home Gnome researchers said while Chicago is larger than St Louis, it has had more continuous growth with investments in public transportation and newer infrastructure.

In Kansas City, which had the third-highest risk, only two percent of homes with lead paint have been renovated to remove it in the past 20 years, the health department estimates. 

The city received a $6.4million grant last year from the US Department of Housing and Urban Development (HUD) to remove the paint, though this is only enough for about 170 additional homes, the city said. 

On the other end of the spectrum, Gilbert, Arizona, had the lowest risk of lead paint exposure, scoring 29 out of 100. 

In the city of 275,000, which is about 20 miles outside of Phoenix, roughly one in four homes were built between 2010 and 2020, minimizing their risk of having lead paint. 

Meanwhile, just four percent of homes in Arizona as a whole were built prior to 1940.