Black Mould
and Your Health

Last reviewed September 2026 by Tony Murphy, Founder & Managing Director. We update these guides in place rather than letting them go stale.

What Does Mould Do to Your Health?

The NHS position is that damp and mould affect the respiratory system, the immune system and the skin. Mould produces allergens, irritants and — in some species — toxic substances, and inhaling or touching spores can provoke a reaction.

In practice the commonly reported effects are respiratory symptoms such as wheezing, coughing and worsened asthma; allergic reactions including sneezing, runny nose, red eyes and rashes; increased frequency of respiratory infections; and, over sustained exposure, a measurable effect on general wellbeing and sleep.

Government guidance for rented housing providers is explicit that these risks are real and that damp and mould should not be treated as a cosmetic or lifestyle matter.

Who Is Most at Risk?

Risk is not evenly distributed, and this is the part that matters most when deciding how urgently to act.

• Babies and young children — developing airways, higher breathing rate relative to body size, and more time spent at floor level.
• Older adults, particularly with existing respiratory conditions.
• People with asthma, COPD or allergies, where mould is a well-recognised trigger.
• People who are immunocompromised — undergoing chemotherapy, on immunosuppressants, or with a condition affecting immune function.
• People with existing skin conditions such as eczema.

If mould is growing in a bedroom used by anyone in these groups, treat it as urgent. That is not a sales position; it is what the guidance says.

Does Bleach Kill Mould?

Partly, and less than people assume. On a hard, non-porous surface such as tile or glass, household bleach will kill surface growth effectively.

On porous materials — plaster, plasterboard, wallpaper, timber, grout — it works considerably less well. The active chlorine stays largely on the surface while the water content soaks in, and the mycelium below the surface survives. The visible black staining disappears, which reads as success, and the colony regrows.

Biocidal treatments formulated for mould are designed to penetrate porous substrates and kill the growth rather than bleach the pigment. That is what we use, and where contamination has gone beyond the surface we cut out and replace the affected plaster or plasterboard instead.

Can You Paint Over Mould?

You can, and it is among the most common false economies in domestic property. Anti-mould paints have a genuine role — as the final step on a surface that remains higher-risk after the cause is fixed and the contamination removed.

Applied over live growth, the coating hides the problem for a few months while the mould continues underneath. The moisture source is untouched, so it reappears, and you end up stripping more material than if it had been dealt with properly.

What Actually Removes It?

1. Find and fix the moisture source. Condensation, cold bridging, a ventilation failure or an underlying damp defect. Nothing else on this list is worth doing first — see rising damp or condensation.
2. Remove the contamination. Biocidal treatment on sound surfaces; cut out and replace where growth has penetrated.
3. Address the conditions. Improve extraction, add a PIV unit, insulate cold reveals — whatever the survey identified.
4. Make good, then protect. Reinstate and, where appropriate, finish with an anti-mould coating.

Mould that returns within a winter means step one was wrong. That is the test of whether a diagnosis was right.

What About Cleaning It Yourself?

For a small patch — less than about a third of a square metre, on a hard surface, with no vulnerable occupants — cleaning it yourself is reasonable. Ventilate the room, wear gloves and an FFP2 mask, avoid brushing or vacuuming dry growth because that disperses spores, and bag the cloths afterwards rather than rinsing them in a sink.

Do not attempt it yourself if the area is large, if it keeps returning, if it is in a bedroom used by someone vulnerable, or if there is an underlying damp problem you have not identified. And note that cleaning treats the symptom — the reason it grew there has not changed.