How Does Bleach Kill Mold?

How Does Bleach Kill Mold?
How Does Bleach Kill Mold? (Image: Renata Horvat,

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Bleach and Mold Abatement

Bleach can kill common molds on nonporous surfaces, making it a convenient household tool to combat mold and mildew. Bathroom showers and tubs, counter tops and toilets are areas that allow chlorine bleach to sit for the time it takes to penetrate the mold cell walls.

Bleach should not be used on metals because of its corrosive nature. It should never contact wiring, nor should it be used in HVAC systems.

Wood and wood-based building materials, ceiling materials, insulation, dry wall and flooring are areas in the home damaged by leaks and flooding. These slow-drying areas need immediate attention to prevent or abate mold and mildew, but bleach should not be used on these porous surfaces.

Active Ingredients of Chlorine Bleach

Sodium hypochlorite (NaOCI) is the active ingredient in bleach. Chlorine bleach forms sodium ions (Na+), hypochlorous acid (HOCI) and hypochlorite ions (OCI-) when diluted in water. HOCI and OCI- are oxidizing agents.

Action of Bleach on Mold Cells

Common molds occurring inside the home include penicillium, cladosporium, aspergillus and alternia. The cell walls of these molds are made up of chitin and glucan. When the chlorine compounds are able to penetrate these walls, they destroy the functions of the membrane and the cells' proteins.

The HOCI (hypochlorous acid) penetrates the walls and the OCI- (hypochlorite ion) breaks down the membranes.

The bleach inactivates the mold and neutralizes surface proteins.

How to Use Chlorine Bleach to Kill Mold

Bleach is easily spent oxidizing any bacteria on the surface before it gets to the wall of the mold. It is important to clean the area thoroughly before attempting to use bleach to kill the mold.

Combine ¾ cup of chlorine bleach with a gallon of water. Apply the solution to mold that is growing on a clean, hard, non-porous surface. The diluted chlorine bleach must be in contact with the mold for a minimum of five minutes, but ideally up to 30 minutes, before it is rinsed off.

Inactive mold spores will be left behind, and those must then be cleaned away. Be careful, as even the dead mold spores can trigger an allergy.

To prevent the mold and mildew from quickly growing back, it's important to completely dry the area immediately. The bleach will kill the existing mold when used appropriately, but will have no future effect to prevent a new growth of mold.

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