Mold spores are killed by chemical disinfectants like bleach and hydrogen peroxide, heat above 140°F, and UV-C light. But killing spores is only half the job. Dead mold spores still trigger allergic reactions and respiratory irritation, so physical removal matters just as much as the killing agent you choose.
Bleach on Non-Porous Surfaces
Sodium hypochlorite (household bleach) is one of the most effective and accessible mold killers. A 2.4% solution, roughly equivalent to diluted household bleach, produces a 99.9% to 99.9999% reduction in culturable mold counts after just five minutes of contact on non-porous surfaces like tile, glass, and sealed countertops. On porous ceramic, you need about ten minutes of contact time for the same result. Spore-related allergen levels drop by an average of 95.8% in as little as 30 seconds.
The catch is porosity. Bleach works on surfaces it can fully contact, but mold growing inside drywall, wood, or fabric sends its root structures (hyphae) deep into the material. The bleach contacts the surface mold but can’t reach what’s embedded below. For porous materials with heavy mold growth, removal and replacement is often more effective than chemical treatment.
Hydrogen Peroxide
Hydrogen peroxide is active against fungi, bacteria, viruses, and spores. Its effectiveness depends heavily on concentration and contact time. A 0.5% accelerated hydrogen peroxide formula kills fungi within five minutes. The standard 3% hydrogen peroxide you’d find at a drugstore can kill bacterial spores, but it needs roughly 150 minutes of wet contact to do so. Higher concentrations work faster: a 10% solution achieves a complete kill of one million spores in 60 minutes.
For household mold cleanup, 3% hydrogen peroxide sprayed directly onto the affected surface and left to sit for 10 to 15 minutes is a reasonable starting point for light contamination. It has the advantage of breaking down into water and oxygen, leaving no toxic residue, which makes it a better option than bleach for surfaces near food preparation areas or in poorly ventilated rooms.
Quaternary Ammonium Compounds
Quaternary ammonium compounds, often listed as “quats” on product labels, are the active ingredient in many commercial disinfectant sprays and wipes. At low concentrations (0.5 to 5 parts per million), they inhibit mold growth without killing it. At higher concentrations of 10 to 50 parts per million, they become actively lethal to fungi, though effectiveness varies by organism and formulation. Many EPA-registered antimicrobial products for indoor use rely on quats as their primary active ingredient.
Heat
Most mold species are heat-sensitive. Temperatures between 140°F and 160°F (60°C to 71°C) destroy the majority of yeasts and molds. This is why hot-water washing of fabrics, steam cleaning, and heat-based drying systems can eliminate mold from clothing, upholstery, and other washable materials.
Some mold species, however, produce heat-resistant spores that survive standard heating. One well-documented example, Byssochlamys fulva, requires a full minute at boiling temperature (212°F / 100°C) to die, and has been known to survive thermal processing in canned foods. If you’re using heat as your mold-killing method, sustained exposure matters more than peak temperature. Running contaminated items through a hot dryer cycle or using a steam cleaner with prolonged contact gives you the best results.
UV-C Light
Ultraviolet light in the UV-C range (around 254 nanometers) damages the DNA of mold spores, preventing them from reproducing. The dose required varies by species. Aspergillus niger, one of the more UV-resistant common molds, needs roughly 220 millijoules per square centimeter to achieve 99% inactivation. Penicillium species are more sensitive, requiring about 124 millijoules per square centimeter for the same result.
Consumer UV-C wands and air purifiers exist, but their real-world effectiveness depends on how long the light contacts the spore and from what distance. UV-C works best in controlled settings like HVAC systems, where air passes slowly through a chamber with continuous UV exposure. A quick pass with a handheld wand over a moldy surface won’t deliver enough energy to reliably kill spores embedded in textured materials. UV-C is also a direct hazard to skin and eyes, so any device should be used according to its safety instructions.
Vinegar and Essential Oils
White vinegar (acetic acid) is a popular home remedy for mold, but the evidence for its sporicidal power is limited. Acetic acid does inhibit mold growth by crashing the internal pH of fungal cells, but it takes relatively high concentrations to do so. In laboratory testing, the minimum inhibitory concentration of acetic acid against Aspergillus niger was 80 millimolar at pH 4.0, and acetic acid was dramatically less toxic to mold than other weak acids like sorbic acid, by a factor of 14 to 58 depending on the species. Household vinegar (typically 5% acetic acid) may slow surface mold on kitchen counters, but it’s not a reliable spore killer for serious contamination.
Thymol, the active compound in thyme essential oil, has documented antifungal properties and is the basis for some EPA-registered botanical disinfectants. Tea tree oil also shows antifungal activity in lab settings. The practical challenge with essential oils is consistency: concentrations vary between brands, and there’s no standardized household protocol with the kind of peer-reviewed kill rates you see for bleach or hydrogen peroxide. They can supplement your cleaning routine for minor mold, but shouldn’t be your primary tool for a significant mold problem.
HEPA Filtration for Airborne Spores
Killing mold on a surface often launches spores into the air. HEPA filters capture at least 99.97% of particles down to 0.3 microns, which is the hardest particle size to trap. Most mold spores range from 1 to 30 microns in diameter, well above that threshold, meaning HEPA filters catch them with even higher efficiency than their rated minimum.
Running a HEPA air purifier during and after mold cleanup significantly reduces the number of airborne spores in the room. Professional mold remediators typically use HEPA-filtered negative air machines for this reason. If you’re doing a DIY cleanup, placing a portable HEPA purifier in the affected room and keeping it running for several hours after you finish is a practical step that makes a measurable difference in air quality.
Why Dead Spores Still Matter
Killing mold spores doesn’t eliminate their health effects. Dead spores still contain the proteins that trigger allergic reactions. Inhaling or touching dead mold spores can cause sneezing, runny nose, red eyes, skin rash, and asthma attacks in sensitive individuals. Even in people without mold allergies, dead spore fragments can irritate the eyes, skin, nose, throat, and lungs.
This is why the EPA has never set threshold limits for airborne mold concentrations, and why remediation guidelines consistently emphasize physical removal over chemical treatment alone. The goal isn’t just to kill the mold. It’s to remove the material entirely, clean the surfaces, filter the air, and eliminate the moisture source that allowed growth in the first place. A surface that’s been bleached but still covered in dead mold residue will continue to cause problems for anyone breathing nearby. Wipe, scrub, or vacuum (with a HEPA-filtered vacuum) after applying any chemical treatment to get the dead spores off the surface and out of the air.