Rust
The most common cause of brown spots on a refrigerator is rust, especially in humid regions. As the appliance ages and the paint thins, the metal underneath is subject to oxidization. Rust doesn't just leave unsightly brown spots on your refrigerator; over time, the metal will rust all the way through, leaving holes or cracks in your appliance that will lead to leaks and other structural integrity problems. To determine if rust is the source of the brown spots on your refrigerator, spray the spots with a mild household cleaner and wipe gently with a clean sponge. If the spots do not disappear, even partially, they are signs of rust.
Preventing/Repairing Rust
GE recommends that owners polish their refrigerators frequently to prevent the paint from thinning. Do not use abrasive cleaners or scrubbers on your refrigerator surface. If you find small brown rust spots, cover them with appliance touch-up paint to prevent further corrosion and improve the appearance of the refrigerator.
Everyday Food Residue
Sometimes stubborn brown spots on a refrigerator may be visible signs of kitchen accidents or minor spills. If your daughter pours a glass of iced tea into a glass on the counter next to the refrigerator, for example, she may not notice if a few drops splash onto the side of the appliance. Within a few minutes, the splashes will dry into brown spots. A spill inside the refrigerator can leak out and stain the exterior, too, while a leaky ice dispenser may leave brown spots below the dispensing area. Many brown spots on the refrigerator are the results of dirty hands. A child may have headed straight to the kitchen for a juice box, after emerging from the sandbox, for example, leaving little muddy hand prints near the handle, or you may have opened the door yourself with butter-coated fingertips while mixing a cake.
Removing Dirt
The longer that brown spots resulting from food residue and dirt remain on your refrigerator, the more difficult they will be to remove. If the spots don't come off with a mild household cleaner and a paper towel, mix a few drops of dishwashing detergent in a small bowl of warm water. Apply the mixture to the spots with a sponge and gently scrub the area clean. Remove any lingering suds and thoroughly dry the newly clean refrigerator surface.