...which means MDF is fine if it's entirely clad in a few mm of something more water-resistant, with the MDF just serving as structural infill. (This is how most kitchen cabinetry is made. And they put up with the steam from a pot boiling below them just fine.)
Our kitchen countertops are MDF covered in some sort of laminate. The laminate is great, but the MDF is swelling over our dishwasher and looks hideous. I'd be careful near moisture even if it's covered.
MDF for structural anything? That seems surprising, it's really weak and prone to sagging, and quite heavy. It's about the last thing I'd want to hang on a wall.
