Ask ten people how to remove mold and nine will say bleach. It is the default answer, it has been the default answer for decades, and on the surfaces most household mold actually grows on it does not work.
The reason is structural rather than chemical, and once you see it the whole thing makes sense.
Porous versus non-porous
On a non-porous surface — glazed tile, glass, sealed metal, glossy paint — mold sits on top of the material. There is nothing to penetrate. Bleach kills what it touches, and so does detergent and a scrubbing brush, which is why bleach appears to work.
On a porous surface — drywall, bare wood, ceiling tile, grout, insulation, fabric — the visible growth is the fruiting part of an organism whose filaments run below the surface. To stop it you have to reach those, and this is where bleach runs out.
What household bleach actually is
Household bleach is roughly 5–8% sodium hypochlorite dissolved in water. The active ingredient does not travel well into porous material — it reacts with the first organic matter it meets and is spent. The water it is dissolved in has no such difficulty and soaks straight in.
The result on a drywall patch is a surface that looks clean, because the pigment in the growth has been bleached out, sitting above filaments that have just been watered. The growth returns, and it returns looking like a new problem rather than the same one.
This is why the EPA has not recommended routine bleach use for mold cleanup for years. Its guidance leads with detergent, water and physical removal.
What to use instead
Detergent and water, with scrubbing, does most of the work on any surface. Mold removal is mechanical before it is chemical — you are physically taking the growth off, and dead mold still triggers allergic responses, so removal matters more than killing.
White vinegar, undiluted at around 5% acetic acid, penetrates porous surfaces and kills a wide range of species. Leave it an hour, then scrub and wipe. It is the better choice on drywall and wood despite being the weaker disinfectant on paper.
3% hydrogen peroxide penetrates well too and is a good option on wood and grout. Spray, wait ten minutes, scrub.
On genuinely soaked porous material — drywall gone soft, wet insulation, carpet — none of these save it. It gets cut out and replaced.
One thing never to do
Never mix bleach with vinegar, ammonia or another cleaner. Bleach and acid release chlorine gas; bleach and ammonia release chloramine. Both are genuinely dangerous in an enclosed bathroom. Pick one product and use it alone.
The takeaway. Bleach on tile is fine. Bleach on drywall removes the stain and waters the roots. Use detergent and physical removal first, then vinegar or hydrogen peroxide — and fix the moisture, or it returns regardless.
Check it in your own house
The failure mode is visible on a timescale of weeks, and one patch treated two ways makes the comparison obvious.
Split a small affected area in two
On a porous surface — painted drywall, wallpaper, bare plaster — treat one half with diluted bleach and the other with detergent and physical scrubbing.
Photograph both halves with a date
Immediately after cleaning, both will look clean. The bleach side often looks cleaner, because it has removed the pigment as well as the growth.
Photograph again at four and eight weeks
If the moisture has not been fixed, the bleached side typically returns first and in exactly the same outline, because the growth beneath the surface was never removed.
Do the same on a tile or glass surface
On a non-porous surface both work, and both keep working. That contrast is the whole argument: it is the material, not the chemical, that decides.
Common questions
Is vinegar really better than bleach for mold?
On porous surfaces, yes. Vinegar penetrates into the material where the filaments are, while bleach largely stays on the surface. On non-porous surfaces like tile, both work and plain detergent works nearly as well.
Why does the mold stain disappear but come back?
Bleach removes the pigment without reaching the growth below the surface, so the patch looks clean while the organism is intact — and the water in the bleach has just fed it.
Can I clean mold off drywall at all?
Light surface growth on painted, sound drywall can be cleaned. If the board is soft, stained through, or was wet for days, it has to be cut out and replaced.
What should I use instead of bleach on drywall?
Detergent and mechanical removal — a cloth, a brush and effort. The aim is to physically take the growth off rather than to kill it in place, because dead growth still stains and still sheds. Where the paper facing of the board is affected rather than just the paint on it, no cleaning reaches the problem and the section needs cutting out.
Is bleach dangerous to use on mold indoors?
It carries real risks that are worth knowing: the fumes irritate airways in an enclosed space, it damages many surfaces, and mixing it with ammonia-based cleaners produces toxic gas. Given that it also underperforms detergent on the surfaces most household mold grows on, there is not much left to recommend it for this job.
Sources
- US EPA — Mold and moisture guidance — the 30–50% range and the 10 sq ft remediation threshold
- ASHRAE Standard 55 — Thermal environmental conditions for human occupancy — indoor comfort and humidity limits
- US DOE 10 CFR 430 — Dehumidifier test procedure — the 2019 move to 65 °F rating conditions