A rust stain on a mattress is probably caused by moisture reaching the inner coils, but consider other possibilities, as well. When removing stains, keep the mattress as dry as possible to avoid further rust stains. Vacuum the mattress monthly to remove dust and dirt, and air it out in the sun annually, if possible.
Moisture can seep through the mattress cover to the metal coils beneath, causing them to rust. Over time, the rust may be visible on the mattress cover. The rust stains won't affect the durability of the mattress, but are unattractive.
To prevent rust from forming on the mattress cover, install a waterproof mattress pad over the cover. Always blot up any spills immediately with clean cloths and use a fan to quickly dry the mattress. Keeping the mattress dry is the best way to prevent rust stains.
Use commercial rust removers that contain oxalic acid or hydrofluoric acid. These products are toxic and may cause serious burns, so read the package directions carefully and wear gloves. A combination of vinegar or lemon juice and salt may remove rust stains, as well. Mix the vinegar or lemon juice and salt to make a thin paste. Rub the paste over the stain until the rust stain disappears. Scrape the paste off and rinse the area with clean water. Blot it well and use a fan.
Consider other materials, such as blood, iodine or benzoyl peroxide, as possible causes of the stain, rather than rust. One unsavory potential cause of reddish brown stains is bedbugs. These small pests are making a comeback in the U.S. as more people travel to undeveloped countries, bringing the bedbugs back home with them. Rust-colored blood spots or dark spots of excrement are signs of a bedbug infestation. If you suspect bedbugs, call an exterminator immediately.