Does Bleach Kill Mould? What Actually Works (UK Guide)

Short answer: bleach kills mould on hard, non-porous surfaces such as glazed tiles, glass and enamel baths. On porous materials such as plaster, plasterboard, timber, grout and silicone sealant it mostly whitens the stain while the growth inside the material survives. That is why mould "comes back" a few weeks after a bleach clean. Government guidance for landlords goes further and says mould and mildew products should be used in preference to bleach.

And even the right product only deals with what you can see. If the moisture that fed the mould is still there, it will return whatever you clean it with.

Why bleach seems to work, then doesn't

Household bleach is mostly water with a small amount of sodium hypochlorite. Sprayed onto a black patch, it oxidises the dark pigment and the wall looks clean within minutes. That visual result is what makes people trust it.

The problem is what happens below the surface. Mould grows as a network of fine threads (hyphae) that push into anything porous. Bleach's active ingredient tends to stay at the surface, while its water content soaks in. So on a plastered wall or a strip of silicone you can end up with:

a lighter-looking surface
living growth still inside the material
extra moisture delivered straight to that growth

A few weeks later the spots reappear, often in exactly the same outline. That is not new mould arriving. It is the same colony that was never removed.

Where bleach is fine, and where it isn't

Glazed tiles, glass, enamel, sealed worktops: bleach works on surface growth, though a mould and mildew cleaner does the same job. Rinse and dry afterwards.
Grout: bleach whitens it but rarely clears it. Use a mould cleaner and a stiff brush; regrout if the staining goes deep.
Silicone sealant: bleach whitens it but the growth stays in the sealant. Cut it out and replace it.
Painted plaster or plasterboard: bleach whitens it but rarely clears it. Use a fungicidal wash, let it dry fully, and fix the cause before redecorating.
Bare timber and window reveals: bleach works poorly. Use a fungicidal treatment and replace badly affected timber.
Carpet, curtains and soft furnishings: bleach is unsuitable. Get them professionally cleaned, or dispose of them if they can't be fully cleaned.

What government guidance actually says

The official guidance, Understanding and addressing the health risks of damp and mould in the home (DHSC, MHCLG and UKHSA, applies to England), sets out a few points that are worth knowing whether you are a tenant or a landlord:

Mould and mildew products should be used in preference to bleach, for health and safety reasons.
Photograph and outline the mould before removing it. The shape and position help find the source.
Larger areas should only be dealt with by qualified professionals.
Removing surface mould alone will not stop it reappearing. The underlying damp has to be found and fixed.
Soft materials such as carpets should be disposed of if they cannot be fully cleaned.

The guidance also suggests a follow-up inspection at least six weeks after treatment, to check whether the problem has really gone.

How to clean a small patch of mould safely

For a small area on a hard or painted surface, this is the sensible approach:

Protect yourself. Rubber gloves, eye protection and a face mask. Open a window. Keep children, pets and anyone with asthma or a weakened immune system out of the room.
Photograph it first, with something in shot for scale. Landlords and tenants both benefit from a dated record.
Don't dry-brush or vacuum it. That puts spores into the air. Work damp.
Use a product labelled for mould, following the instructions on the label, and wipe with a disposable cloth.
Bag the cloths and throw them away.
Dry the surface fully and keep the room ventilated while it dries.

Two safety points that matter more than which cleaner you buy: never mix bleach with other cleaning products, especially anything containing ammonia or acid (some toilet and limescale cleaners), because the combination can release toxic gas. And never use a pressure washer or steam cleaner on mouldy surfaces indoors.

When to stop cleaning and get a specialist

Clean it yourself if the patch is small, on a hard surface and you know why it appeared. Get professional help if:

the mould covers more than a small patch, or is spreading between rooms
it keeps returning in the same place after cleaning
it is on ceilings, behind furniture across a whole wall, or in more than one room
there is a musty smell but you can't see the source (it may be behind panels, under floors or in a loft)
someone in the home has asthma, COPD, a weakened immune system, is pregnant, very young or elderly
the property is rented and the landlord needs evidence of what caused it

A mould remediation specialist will treat the growth, but the useful part of the visit is the diagnosis: condensation, penetrating damp, a leak, or rising damp all need different fixes. If you are unsure which you have, start with our guide to damp surveys versus mould inspections.

For landlords: cleaning is not a repair

A tenant wiping mould with bleach, or a landlord sending someone round to "treat" it, does not resolve a hazard. In England, the updated Housing Health and Safety Rating System includes a baseline indicator that no room should have observable damp or mould over more than 5% of a wall or ceiling surface. Social landlords also have Awaab's Law timeframes to meet for significant damp and mould hazards.

The guidance is also clear that it is unreasonable to blame damp and mould on tenants' "lifestyle choices". Cooking, washing and drying clothes are normal. If a home cannot cope with normal living without growing mould, the building needs work: ventilation, heating, insulation or a repair. See who is responsible for damp and mould in a rented property for the full picture.

FAQs

Does vinegar kill mould better than bleach?

Vinegar is mildly acidic and can help on some surfaces, but evidence for it as a reliable treatment for established mould is limited. A product labelled for mould, used as directed, is the safer choice. Either way, cleaning does not fix the cause.

Is black mould killed by bleach?

"Black mould" is a description of colour, not a single species. On tiles, bleach removes it from the surface. On porous surfaces the same problem applies: the stain fades but growth in the material can survive. Read more in is black mould dangerous, and how do you get rid of it for good?

Will anti-mould paint stop it coming back?

Anti-mould paint can slow regrowth on a clean, dry, treated surface. Painted over live mould, or on a wall that is still cold and wet, it will fail. Fix the moisture first.

How much does professional mould removal cost?

It depends on the area, access and what is causing it. Our mould removal cost guide breaks down typical UK prices.

Does bleach kill mould? What actually works on walls, grout and plasterboard