The red color of modern lipstick can come from synthetically derived pure iron oxide (common iron rust), however most leading brands use the more economical synthetic colors. In the United States, every batch of synthetic dye and pigment must have a sample sent to the US FDA for testing and certification that the batch is pure and its contaminants are below the levels specified by law. Synthetic colors are listed in the ingredients as a code (e.g.: F &D red no 6) and may contain up to 10 parts per million of lead / 3 parts per million of arsenic. There is some controversy over the presence of these trace ingredients, especially since makeup worn on the lips is not just absorbed through the skin, but also swallowed with drinking and eating. Since lowering these levels would make the production and sale of practically all lipstick illegal, and since the FDA has determined that the existing levels are safe, the cosmetic industry continues to produce and sell lipstick.