Several things can cause yellow rings on a mattress. Urine stains can do this, as can previous cleaning processes that you did not rinse out completely. You can clean these stains and should clean them as soon as you notice them. This will result in a cleaner mattress that looks more pristine and smells better. Be careful not to soak your mattress, as this can encourage mold or mildew growth.
Mix 1 cup hot water with ¼ tsp. dish detergent. Do not use soap as this will leave a residue on the mattress.
Dip a sponge onto the solution and wring it out as much as possible.
Rub the sponge over the yellow stain until you've removed as much of it as possible.
Dip a toothbrush into the solution and scrub the yellow stain with it until you remove all of the stain that you can.
Mix 1 cup white vinegar with 1 cup water.
Dip a cloth into the mixture and wring it out.
Rub the cloth over the area. This will help rinse away the soapy solution and it will help remove any odors associated with the stain.
Let the mattress air dry completely.
Sprinkle baking soda over the stain if it smells. Let the baking soda sit for several hours before vacuuming it up.