You can find it in children's toys and jewelery, in pottery and dishware. It's even in your backyard or in the water you drink. But most parents don't think of lead as something that could endanger their children's health.
Now there's new science suggesting otherwise, and doctors like Helen Binns at the Children's Memorial Lead Evaluation Clinic say the message is trickling out slowly to parents and pediatricians alike.
"We now know that lead is a poison at all levels," she said, adding that the prior concept that lead levels had to reach a certain threshold to damage a child's developmental progress or IQ no longer holds true.
It's something mother Siouxie Donnelly said she never thought about.
When she took her bouncy 9-month-old for a wellness checkup she was shocked to be told that baby Lorelei had potentially harmful levels of lead in her blood: nine micrograms.
"I don't think I've ever known anyone to have it, talk about it or worry about it," she said.
And up until fairly recently, Donnelly might have been told not to worry. Parents were routinely told that levels of up to 10 were acceptable. Dr. Binns said that in the late 70s, levels of 15 in children were not unusual.
"It's a problem we think was taken care of long ago," said Anne Evens, the former director of Chicago's childhood lead poisoning prevention program.
But take the example of lead paint in houses.
A majority of Chicago's housing stock was built when lead paint was still in use. Evens said it's still out there in a lot of neighborhoods, sometimes in the soil or in the paint on the exteriors of homes.
And like Dr. Binns, she said there's no such thing as a safe level of lead. In fact, Evens is finishing up research in Chicago Public Schools that shows lead has in impact on IQ even at low levels.
Chicago and some parts of suburban Cook County are still considered high risk areas, where every child should get a blood test for lead at least twice before their second birthday. Doctors say that if you know it's there, you can stop it.
That's what the Donnellys did as soon as they found out about Lorelei. They lived in a decades-old building and suspected the windowsills in the baby's play area might be the cause. They closed the windows and within weeks, Lorelei's mom said her baby's level began dropping.
Chicago has now lowered what it considers acceptable lead levels to five micrograms.