Freezing kills mould

Does it work?

Does not work

Refuted as stated, and the refutation comes from a source that uses freezing as a technique itself: freezing does not kill mould, whatever else it is good for. Freezing an affected item to stop damage while a plan is made is sensible; believing it has killed anything is not, and the difference decides whether the item goes back on a shelf or gets dealt with.

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

Cold is assumed to kill organisms as heat does. The mechanism as far as it goes is real: low temperature arrests metabolism and halts germination and hyphal growth. What the assumption adds without support is lethality. Fungal spores are structures adapted to survive adverse conditions — the same guidance describes them as often water repellent and resistant to desiccation — and surviving cold is one of the things they are for. Freezing therefore suspends the process at whatever stage it had reached, and the process resumes when the conditions that suspended it are removed.

Background

The technique circulates widely and it does something real, which is why it survives. It is not what people think it does. The federal conservation guidance addresses freezing directly and its sentence is unambiguous: extreme cold, freezing, and heat DEACTIVATE spores or spore growth BUT DO NOT KILL THEM, and if temperatures go up after cold, spores can be reactivated and mould will continue to grow. Deactivation is a pause rather than an end. That makes freezing genuinely useful for one purpose the guidance itself uses it for — halting active growth on an item that cannot be treated immediately, so damage stops while a plan is made — and useless as a cure. Two findings compound it. Killing mould does not eliminate all health hazards, because inactive mould still causes reactions in sensitive people. And the growth has already stained permanently. What resolves it is what resolves any mould problem: remove the growth physically and change the moisture conditions, or accept that it resumes when the item warms.

Conditions

• Applies to items placed in a domestic freezer
• Growth already present

What it does not do

• It halts growth rather than ending it, and warming reactivates what survived.
• It does nothing about the staining, which the same guidance describes as permanent.
• It does not address the moisture that produced the growth, so an item returned to the same place resumes.

What to use instead

• Moisture control — The treatment for mould that is not a cleaning product. Every authority puts it first, and it is the only thing that stops the problem recurring.
• Dehumidifier — Not a cleaning tool at all, and the most effective single purchase against mould — because it treats the cause the spray bottle cannot reach.
• Fungal spores — Already everywhere, water-repellent, and resistant to drying out. Removing them is not the goal, because it is not achievable — denying them moisture is.
• Moisture control and recurrence — Three separate health authorities lead with the same instruction, and it is not a cleaning instruction: fix the water. Clean without fixing it and the mould comes back, and the cleaning was never the failure.