There's no need to use harsh chemicals like ammonia or bleach to remove a mildew smell under a sink and dishwasher. Vinegar, hydrogen peroxide and baking soda deliver a one-two-three knockout punch to most types of household mildew. All three are natural substances that will not harm family pets or small children, and they are safe for the environment. Follow these simple steps to eliminate mildew and its odors.
Remove everything from under the sink. Discard items that are are damp or have mildew on them. If possible, move the dishwasher out from under the countertop.
Fill one spray bottle with distilled vinegar -- white vinegar -- and the other with hydrogen peroxide. Use them both at full strength; do not dilute them, and don't mix both in one container. Mixing diminishes their effectiveness.
Spray the affected areas with the vinegar. Allow it to sit for 10 to 15 minutes, but don't allow it to dry. Although the odor of the vinegar may be unpleasant for a short time, it is completely nontoxic, and the smell dissipates in just a few minutes. Wipe the areas clean with a damp sponge or towel.
Spray the same areas immediately with hydrogen peroxide. Allow this to sit for the same amount of time, and then wipe dry. Heavily affected areas may require a second application.
Dissolve a quarter-cup of baking soda in a gallon of water, and clean the areas with a sponge. Allow the areas to dry completely. A fan will shorten the drying time. Place an open box of baking soda under the sink to absorb future odors. Replace the baking soda every 30 days.