In the past, lead was considered to be a very useful metal. It was implemented in paint to get more vivid and long-lasting colors. It was used in pipes either to make an easy seal or for the entire pipe since it could be easily shaped as needed. The problem is that lead is very harmful to your health. It has been linked to neurological damage, kidney problems, and birth defects just to mention a few of the issues that lead can cause.
This might not be a problem for you, but if you live in an older home, it is a good idea to be aware of the danger lead poses, as well as where it possibly could be located.
If you have old paint that flakes in an odd way, kind of looking like scales, you might be dealing with lead paint. It is important to be extra careful if you renovate a room that could have lead paint, since sanding it can cause a cloud of fine dust that contains lead to fill the room.
If you have pipes in your basement that you can easily scratch with a sharp object, then you are probably dealing with lead pipes as well. If these are connected to your water supply, you might be ingesting lead whenever you are drinking water. If you are uncertain, it is a good practice to err on the side of caution and get a professional to check it out for you.