A door gasket is a moulded strip, typically PVC or a similar flexible material, with a magnetic insert that pulls it against the steel cabinet face. Its bellows-like profile lets it adapt to small misalignments so the seal stays airtight even when the door is not perfectly square.
Gaskets wear out. Constant opening, cleaning chemicals, grease, kitchen heat and sharp tray edges crack and tear them. A damaged gasket lets in warm, humid air, which raises running cost, makes the compressor run longer and builds frost or condensation around the door. In a freezer, ice on the inner frame is a classic sign.
A simple test: close the door on a sheet of paper at several points around the frame. If it slides out easily, the seal is weak there. Clean gaskets regularly with mild detergent and warm water, avoid harsh solvents, and replace damaged ones promptly. Most gaskets push into a groove or are screwed on and can be replaced without opening the sealed system.