Photo by @christinacorso on twenty20.com

These things mean something beyond the appearance. Checking the humidity conditions behind the walls can lead to find broken pipes or structural construction problems.

In the case of stains, germs (fungi, viruses, and bacteria) can be a part of the consequences if you are careless. If cleaning seems not to be enough, maybe it means that refinishing is in order.

Refinishing is easy, as it consists of the removal of the top layer of the tub, which is cleaned and a new coating is then applied, taking away the problem. It is, anyhow, easier to be made in older bathtubs, such as the cast iron or steel ones. Acrylic and fiberglass, for instance, are easy to be refinished too, but sometimes they are so common and cheap that it is important to get the estimate costs of both replacing and refinishing, and compare them.