Until 1977, lead was often added to interior paint to make it more brilliant, durable and moisture-resistant. It can be present at exceptionally high levels in paints used before the 1960s. It was also added at high levels to outdoor paint until 1992.
Homes first built in the 1930s and earlier may have accumulated over 200 kilograms of lead, which poses little threat if undisturbed. However, replacing old windows or drilling into walls to blow in insulation, for example, can contaminate the house with lead dust, which is especially dangerous for babies and young children, who tend to crawl on the floor and put their hands and other objects in their mouths.