Mould needs bleach

Does it work?

Does not work

Refuted, on evidence from the federal environmental regulator. The claim as stated is that bleach is REQUIRED and that detergent will not do. Two public authorities give detergent and water as the method, one of them explicitly does not recommend biocides as routine, and neither treats bleach as necessary. That is a refutation of the necessity. It is NOT a finding that bleach fails to kill mould, which it plainly does.

This is a verdict on whether the technique is effective. Whether it is safe on a particular surface is a separate question, answered below.

Where not to use it

Why it works

Sodium hypochlorite oxidises the cell structures of micro-organisms, so it does kill mould on a surface it reaches. Three things are usually left out, and the regulator states the first of them outright. Killing is not removing: dead mould is still a residue and still causes allergic reactions in some people, so a surface left dead but uncleaned is not a surface dealt with. On a porous material a surface treatment does not reach growth that has gone into the crevices, which is why the answer for porous items is disposal rather than a stronger cleaner. And nothing applied to a surface addresses the water that produced the growth, so a treated surface that stays damp regrows regardless of what was used on it.

Background

This is the most confidently repeated instruction in domestic mould advice, and the authority everybody invokes addresses it directly in its fuller booklet. Using a chemical or biocide that kills mould — chlorine bleach is the agency's own example — is NOT RECOMMENDED AS A ROUTINE PRACTICE during mould cleanup, with room left for professional judgement in cases such as immune-compromised occupants. That is a recommendation against, not a prohibition, and the two are different. The sentence that settles the claim comes immediately after: DEAD MOULD MAY STILL CAUSE ALLERGIC REACTIONS, SO IT IS NOT ENOUGH TO SIMPLY KILL IT — IT MUST ALSO BE REMOVED. A treatment that kills without removing has done half a job, and that is precisely what a bleach spray left to dry does. The method both the agency and a state health department actually give is to scrub the growth off hard surfaces with detergent and water and dry completely. What no cleaner changes: porous materials such as ceiling tiles and carpet may have to be thrown away, and mould on a surface that stays wet is a symptom of the water problem rather than a cleaning failure.

What it does not do

• The environmental regulator explicitly does not recommend biocides such as chlorine bleach as a routine practice
• Detergent and water is the method both the regulator and a state health department actually give
• Killing growth is not removing it: the regulator states that dead mould still causes allergic reactions and must also be removed
• Porous materials such as ceiling tiles and carpet may have to be discarded rather than cleaned
• No surface treatment addresses the moisture that caused the growth
• Areas larger than about ten square feet are beyond what the guidance treats as a householder job

What to use instead

• Detergent — A surfactant-based cleaner. The general-purpose answer for greasy and particulate soil, and the correct first choice far more often than any specialist product.