Gado Labbo holds her 5-year-old son, Yusuf, at a clinic in Dareta, Nigeria. In 2010, when Yusuf first entered the clinic, he had a blood lead level 30 times higher than the amount the Centers for Disease Control and Prevention considers dangerous. David Gilkey/NPR hide caption

itoggle caption David Gilkey/NPR

A child wearing the traditional eyeliner kajal peeps from behind a door in Allahabad, India. Rajesh Kumar Singh/AP hide caption

itoggle caption Rajesh Kumar Singh/AP

A boy works at an illegal gold mine in northern Nigeria. Lead from these mines has sickened thousands of children in the region. David Gilkey/NPR hide caption

itoggle caption David Gilkey/NPR

Old paint is the chief source of lead poisoning in children. iStockphoto.com hide caption

itoggle caption iStockphoto.com