Lead poisoning is an environmental disease that can cause brain damage. It can result in reduced IQ and attention span, learning disabilities, developmental delays and a range of other health and behavioral effects. Lead poisoning is considered a housing-based disease because most exposures for young children occur in homes built before 1978. More than half of the homes built before 1978 contain some lead-based paint and is more common in homes built before 1960. In 1978, lead was banned from being added to paint and varnish for residential use. However, because lead was added to products for many years, the lead is still present in the underlying layers of paint and varnish.