Exposure to chlorine in swimming pools, sunscreen products and natural oils from the body all contribute toward the discoloration of a white swimsuit. Yellow discoloration and other stains cause the swimsuit to look dirty, even when it's been cleaned. Although chlorine bleach is often used to whiten and brighten white fabrics, the synthetic fabric typically used in swimsuits can become weakened and stretched out as a result of using chlorine bleach.
Rinse your white bathing suit under cool water immediately after taking it off. This helps to rinse out chlorine that can yellow and dry out the fabric.
Apply prewash stain remover to any areas that have yellowed or have discoloration from sweat, natural body oils or suntan lotion. Allow the prewash stain remover to soak into the dampened fabric for an hour.
Mix one tablespoon of laundry detergent for fine washables in one gallon cool water in a bucket or sink. Soak the bathing suit in the detergent solution for 10 to 15 minutes to loosen stains. Dunk the bathing suit up and down in the water, to agitate.
Empty the detergent solution out of the bucket then fill it with cool water. Dunk the swimsuit in and out of the cool water to rinse the detergent out of the fabric. Fill the bucket with clean rinse water and continue to rinse the swimsuit, until the rinse water remains clear.
Wring out the bathing suit gently. Lay the wet suit on a clean towel. Roll the towel up, with the swimsuit inside, and press on the towel to absorb moisture out of the swimsuit. Place the swimsuit on a clean towel and allow it to air dry. A white swimsuit can be placed in direct sunlight to allow the sun to further bleach any remaining discoloration. Turn the swimsuit over halfway through the drying process, so the backside can be sun-bleached, as well.