Thinking of Using Bleach on Mould? Here Are 10 Questions You Should Ask First.

It’s easy to panic when you see mould growing in your home—and just as easy to reach for bleach or a “mould killer” spray and try to wipe it away. Plus you can’t walk down an aisle at Bunnings or the supermarket without seeing a bunch of them - so they must do something…right?

Unfortunately, it’s not quite that simple.

Here are 10 important questions to consider before using bleach or any conventional "mould-killing" product:

1. Did you know mould is already about 75% dead by the time you can see it?

Yep, it’s mostly dead anyway, even before you attack it with the bleach. The problem isn’t whether it’s dead or alive - it’s the fact it’s there at all.

2. Did you know bleach kills about 95% of mould, but leaves the strongest 5% behind?

That surviving 5% is often the most resistant and aggressive - and it’s left there ready to start growing again.

3. Did you know dead mould can be just as toxic as living mould?

Even if you kill it, the dead mould fragments and spores still carry mycotoxins and inflammagens that can trigger symptoms—especially in people with CIRS or mould-related sensitivities. TLDR: dead mould is just as toxic is living mould. Mould needs to be physically removed, not just killed.

4. Have you identified the source of moisture?

Mould doesn’t appear without a moisture problem. Killing surface growth won’t solve anything if you haven’t addressed the leak, humidity, or condensation or water intrusion issue that allowed it to grow in the first place.

5. Did you know non-porous surfaces can be safely cleaned with just hot soapy water and a microfibre cloth?

For non-porous surfaces that are easily cleaned - like sealed tiles, glass, or metal, there’s no need for harsh chemicals. A microfibre cloth traps spores effectively, and hot soapy water is enough to remove them—without triggering a toxic defence reaction from the mould.

6. Did you know using harsh chemicals like bleach can cause mould to release defence chemicals?

Moulds can emit mycotoxins, MVOCs (microbial volatile organic compounds), or spores when they feel threatened. Using strong chemicals like bleach may cause them to go into “survival mode” and release even more harmful by-products into the environment. Using hot soapy water and a microfibre cloth (where appropriate to clean the mould like a non-porous surface) helps to prevent making the mould ‘angry’.

7. Did you know bleach doesn’t penetrate porous materials like gyprock or wood?

It might discolour surface growth, but if the mould is inside the wall or ceiling cavity, behind the skirting boards, or even the shower wall - then bleach won't reach it. These materials need to be physically removed, not wiped down.

8. Did you know bleach itself is toxic?

Bleach releases chlorine-based fumes that are harsh on lungs, eyes, and skin—especially dangerous for children, pets, and people with respiratory or immune sensitivities. Really, it has no place in a healthy home.

9. Did you know bleaching mould only removes its colour?

It might look like it's gone, but the structure is often still there. In fact, if we take a lab sample and add blue dye, the “invisible” mould lights up under a microscope.
Bleach hides mould—it doesn’t fix it.

10. Did you know real mould remediation starts with correcting the moisture source?

Proper mould remediation isn’t about spraying and praying. It’s about:

• Identifying and correcting the moisture source

• Safely removing contaminated materials

• Cleaning remaining surfaces to remove spores and fragments

• Restoring normal fungal ecology—not just hiding it

If you're dealing with mould in your home, skip the bleach and start by understanding the cause. Where it’s appropriate to clean - HEPA vacuum the surface (optional), then use a hot, soapy microfibre cloth (1L water to 5 drops dish soap) to wipe, then wipe over it again with a dry microfibre. Bin the cloth you used to wipe it. That’s all! No vinegar, essential oils, or anything else required. What works to remove mould and mycotoxins is a surfactant-based product, which is all dish soaps.

And if you’re doing this - PLEASE WEAR A MASK.

I can’t stress this enough (as someone who learnt this lesson the hard way).

Sometimes it’s easy to work out what the source of moisture is that’s allowing mould to grow, and other times it’s more difficult and requires an inspector. Surface treatments like Bleach and Exit Mould might make an area look better temporarily, but real solutions start with moisture control, proper cleaning methods, and in some cases, professional mould remediation.