Mildew thrives in damp places and, since a shower door usually remains closed for extended periods and the seal doesn't fully dry, it will often stick to the shower door seal. The seal of a shower door also collects soap scum and hard water stains. All of these things will a vigorous cleaning effort to remove.
Combine 1 cup of chlorine bleach with 1 gallon of hot water in a 1-gallon bucket. Wear gloves to protect your hands from the solution and any mould or mildew that you may encounter.
Scrub the seal with an old toothbrush dipped in the diluted bleach solution. Scrub the seal area and all the edges to break apart any residue build-up.
Rinse the area with clean water. Scrub the shower seal with a sponge to remove any grime.
Remove stubborn stains by combining an equal amount of baking soda and water to form a paste. Use the toothbrush to scrub the paste over the seal.
Dilute 1 cup of white vinegar with 1 cup of water. Dip a clean sponge in the solution and wipe it over the seal to remove the baking soda. This will not only remove stubborn stains but it will also remove any lingering odours.