Like most materials that aren't maintained or cleaned properly, silicone sealant or caulking will get dirty over time. You'll most often see a yellow discolouration on the silicone caulking used on your bath and shower, which is caused by dirt, grime and moisture. Unfortunately, you won't be able to return your silicone to its natural white or clear appearance with soap and water; you'll have to use a bleaching solution.
Pour some washing-up liquid on your sponge and wet the sponge with warm water.
Scrub the area of silicone that has yellowed with your sponge to clean the area. Rinse your sponge with hot water and wipe down the area to remove excess soap. Dry the yellowed silicone with a paper towel.
Put on your rubber gloves, and fill a bucket with the warm water and bleach. Stir the solution with a large spoon.
Dip your scrubbing brush in the bleach solution and scrub the yellowed silicone area for a few minutes. Ensure each yellowed area has some of the bleach on it.
Leave the bleach solution on the yellowed silicone for about 20 minutes.
Scrub the yellowed silicone area again with your brush for a few minutes.
Rinse the silicone with water and dry it with more paper towels.