Lead paint has been a major health issue for many hundreds of years. well before it was required to be discontinued in paints and certain other products in 1978, society knew there was an issue.
People who were exposed to lead products were known to die, and have many health issues – so it was relatively easy (over time) for them to figure it out. But it was a very durable and useful product – so many did not want to give it up.
Many people assume that if you buy a home after 1978 that it will not have a lead paint issue – but that is not necessarily true. While production had to stop in 1978, dealers were allowed to sell out their stock for a period of time. Contractors tended to buy up as much as they could in that time period, and used that lead paint for several years afterward.
Lead was also used in other products, such as window glaze, certain metallic items, and other components of the home. Also, it was still used (legally) in aluminum siding well into the 80’s.
So, while 1978 is a good benchmark, lead paint and products have been found in homes even built in the early 90’s. So be safe, have things professionally tested, and be careful with your family’s health.