There are a few possible reasons why your bathroom walls might be sweating yellow. It could be due to a build-up of soap scum or mold, or it could be a sign of a more serious problem like a water leak.
If you think that soap scum or mold might be the cause, you can try cleaning the walls with a bleach solution. If the problem persists, it's best to call a professional to take a look.
A water leak is a more serious issue. If you notice yellow stains on your walls that seem to be getting worse, it's important to call a plumber right away. A leak can cause serious damage to your home and should be fixed as soon as possible.