What is it?
A proxy for childhood lead exposure risk based on the share of housing built before 1978, when residential lead paint was banned. Older homes, especially poorly maintained ones, can flake lead paint that children ingest.
Why it matters
There is no safe level of lead in a child's bloodstream. Lead exposure causes permanent neurological damage, reduced IQ, behavioral problems, and lower lifetime earnings.
Reference value
Counties where more than 50% of housing was built before 1978 carry meaningfully higher childhood lead exposure risk, especially when overlaid with poverty (lower remediation budgets).
Data source
U.S. Census ACS housing-age data