Bleach vs. Vinegar for Mold: What the Studies Found

What did the studies find about vinegar?

• 2015, two common indoor molds. Vinegar at 4.0 to 4.2% acetic acid stopped the growth of Penicillium chrysogenum but had no effect on Aspergillus fumigatus. The authors concluded vinegar has limited antifungal action and may not work against the range of molds found indoors (Rogawansamy et al., 2015).
• 2018, five molds from indoor and outdoor air. Vinegar at 4% acetic acid showed limited or no antifungal activity against all five. The researchers called the result surprising, since vinegar is often recommended for mold (Schroder et al., 2018).

Both tests were done on lab plates, not on drywall or wood. The 2015 authors note that because vinegar doesn't stay on surfaces long, its use may be limited to non-porous materials (Rogawansamy et al., 2015).

What did the studies find about bleach?

• 2004, nine kinds of household mold. Bleach at 2.4% sodium hypochlorite left no mold that could be grown in 10 of 10 trials, after 5 minutes on non-porous surfaces and 10 minutes on porous ceramic. It also cut Aspergillus fumigatus allergen levels by more than 90% (Reynolds et al., 2004).
• 2005, mold grown on building materials. Diluted bleach and a bleach-based bathroom cleaner, sprayed on Aspergillus fumigatus growing on building materials including oriented strand board, killed the mold. Three of four mold-allergic volunteers no longer reacted to the treated board in skin tests (Martyny et al., 2005).
• Mold grown on drywall. After hypochlorite was sprayed on moldy drywall, no Alternaria colonies grew back from surface samples at the three highest of the four strengths tested (World Allergy Organization Journal).
• 2018, five molds. Bleach had strong antifungal activity against four of five molds at first, but the effect faded over the following days (Schroder et al., 2018).

Why does bleach struggle on wood?

A review of 109 studies found hypochlorite worked far better on spores floating in water than on plastic, and worst of all on wood. The authors point to two causes. First, material on and in the surface uses up the chlorine before it reaches the fungus. Second, rough, uneven surfaces keep the bleach from touching everything (Copes and Ojiambo, 2021).

A Mississippi State University wood researcher adds several problems with bleach on building materials (Mississippi State University):

• Building materials soak up large amounts of it and can slowly release chlorine gas into the house.
• Long exposure loosens the fibers of wet wood, essentially pulping the surface.
• It is corrosive.
• Bleach isn't labeled for treating wood or other porous building materials.

So the accurate version of "bleach doesn't kill mold" is narrower. Bleach kills mold it reaches, but it does poorly on wood and isn't meant for porous building materials.

What's the chemistry behind each one?

Bleach is sodium hypochlorite in water. Its killing action comes from hypochlorite and hypochlorous acid, which are strong oxidizers (Copes and Ojiambo, 2021). Oxidation also breaks apart the mold proteins that trigger allergies (Reynolds et al., 2004; World Allergy Organization Journal). The same reactivity is its weakness: other organic material uses it up (Rogawansamy et al., 2015).

Vinegar is a weak acid, mostly water with a few percent acetic acid. Weak acids work better the more acidic the conditions are. In a food-safety study on Aspergillus molds, each 0.5 rise in pH roughly doubled the amount of acid needed to stop growth, and some species resisted far more than others (Food Research International, 2016). That fits the household tests, where vinegar worked against one mold and not others.

Where does the 82 percent vinegar claim come from?

Many websites say vinegar kills 82% of mold species. We couldn't find a published study behind that number. The peer-reviewed tests we found, described above, showed a clear effect against only one of the seven molds tested, and limited or no effect on the other six (Rogawansamy et al., 2015; Schroder et al., 2018).

Why isn't killing mold enough?

Dead mold can still cause allergic reactions, so it isn't enough to kill it. It has to be removed (EPA). The EPA also notes that a background level of mold spores will always remain, and those spores won't grow once the moisture problem is fixed (EPA).

What that means in practice:

• On hard surfaces, scrub the mold off with detergent and water, then dry (EPA).
• Moldy porous materials like ceiling tiles and carpet may have to be thrown away (EPA).
• Fix the leak or humidity first, or the mold comes back (EPA).

See mold after water damage for the full cleanup steps, and the mold remediation cost guide for bigger jobs.

Is it safe to mix bleach and vinegar?

No. Mixing bleach with any acid, including vinegar, releases chlorine gas. Chlorine gas can cause coughing, trouble breathing, chest pain and eye and throat irritation, and it can be life-threatening in enclosed spaces (Transport Canada). Never mix bleach with ammonia either, because that also creates toxic fumes (EPA). If you use one, rinse the surface well before you use the other.

Common questions

Related guides

• Mold after water damage 6 min
• Mold remediation cost 5 min
• Water-damaged drywall 6 min
• Black mold 6 min

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