When the non-stick coating of a Teflon pan has worn off, and only the bare metal remains, it is generally not recommended to continue using the pan for cooking. Here's why:
Potential ingestion of coating: Teflon is a brand name for a type of non-stick coating called polytetrafluoroethylene (PTFE). When the coating on a Teflon pan deteriorates or scratches off, there is a risk of ingesting small particles of the coating along with your food. While consuming a small amount is unlikely to cause immediate harm, long-term exposure to PTFE particles is a concern.
Release of toxic fumes: When Teflon pans are heated to high temperatures without food or with the coating damaged, they can release toxic fumes. The fumes come from the breakdown of PTFE, and inhaling them can cause a condition known as polymer fume fever, resulting in flu-like symptoms.
To ensure food safety, it's best to discontinue using a Teflon pan once the coating has worn off. Instead, consider replacing the pan or opting for alternative cookware options, such as stainless steel, cast iron, ceramic, or enamel-coated pans. These options do not have non-stick coatings and are safe for cooking even if the surface is bare metal.