Lead in old homes comes from paint, dust and pipes — and no blood level is considered safe

Most childhood lead exposure in the United States comes from the home: lead-based paint in housing built before its 1978 residential ban, the contaminated dust that deteriorating paint sheds onto floors and windowsills, and, in some homes, drinking water drawn through lead pipes, solder or fixtures [s3]. There is no known safe level of lead in a child's blood, and the harm to the developing brain is measurable at concentrations once considered unremarkable [s1][s2].

The evidence for low-level harm rests on a 2005 international pooled analysis of seven cohort studies, which modelled how children's IQ changed with blood-lead concentration [s1]. It found a 6.9-point IQ decrement (95% confidence interval 4.2 to 9.4) as concurrent blood lead rose from 2.4 to 30 µg/dL [s1]. The striking feature was the shape of that curve: the loss was steepest at the bottom of the range. The estimated decrement was 3.9 points (95% CI 2.4 to 5.3) going from 2.4 to 10 µg/dL, but only 1.9 points from 10 to 20, and 1.1 points from 20 to 30 [s1]. In other words, the first few micrograms did proportionally more damage than later ones — evidence that undercut the idea of a threshold below which lead is harmless [s1].

What "no safe level" means in practice

The US Centers for Disease Control and Prevention no longer defines a level of concern implying safety below it. Instead it uses a blood lead reference value — currently 3.5 µg/dL — to identify children in the top few percent of exposure who warrant follow-up, and updates that value downward as population exposure falls [s2]. The reference value is a screening trigger, not a safety threshold; the underlying position is that lead has no beneficial role and no demonstrated safe dose in children [s1][s2].

The three home routes

Paint is the dominant source. In homes built before 1978, intact paint is generally not an immediate hazard, but paint that is chipping, peeling or disturbed by renovation generates lead dust and chips that young children ingest through normal hand-to-mouth behaviour [s3]. Friction surfaces — windows that are opened and closed — are common dust generators [s3]. The EPA's guidance emphasises controlling dust through cleaning and using lead-safe practices during any repair or renovation of older housing [s3].

Water is a second route, from lead service lines and older plumbing; running the tap before use and using cold water for drinking and cooking reduce, though do not eliminate, exposure where lead plumbing is present [s3]. Soil near old painted exteriors and busy roads, and some imported pottery, cosmetics and spices, account for the remainder [s3].

The limits of the evidence

The IQ estimates come from observational cohorts, which adjust for but cannot perfectly remove the poverty, older housing and other exposures that travel with lead, and IQ is a population-average measure that does not predict any individual child's outcome [s1]. The pooled analysis established an association with a biologically plausible dose-response, not a guarantee of harm at any given level [s1]. What is not in dispute across the CDC, EPA and the cohort evidence is the practical message: the exposure is preventable, it originates largely in the home, and lowering it — especially for young children in older housing — is where the benefit lies [s1][s2][s3]. This is informational reporting, not medical advice.