Wax seals are designed to last as long as a toilet does. You can expect a life of up to 30 years or more! Normally, you will never find trouble from wax seal failure.
When a wax ring fails, it is easy to identify. Water leaks out from around the base of the toilet. Sometimes, you will also notice the toilet feeling wobbly when the wax ring comes loose.
A toilet's wax ring is used to create an airtight seal to prevent water and sewer gas from escaping from the toilet.