Damp And Mould: How To Identify, Treat And Prevent It

Damp and mould is the most common serious problem in rented housing, and the most commonly mishandled. Tenants get told to open a window. Landlords paint over it. It comes back every autumn.

This guide is the practical one: how to work out what you're actually dealing with, how to treat it safely, and what prevention genuinely works when you can't change the building. If your question is who has to pay to fix it, we've answered that separately in who is responsible for getting rid of black mould.

The short version

• Government guidance says blaming your "lifestyle" is unreasonable. In its own words, the causes are building deficiencies, not normal domestic activity.
• It's a health issue, not a cosmetic one. The effects range from cough and wheeze to, in the most severe cases, death.
• Identify the type before you treat it. Condensation, penetrating and rising damp look similar and need completely different fixes.
• You don't need a doctor's note to be taken seriously. The guidance is explicit that medical evidence is not required before a landlord acts.

Why this matters more than it looks

Damp and mould produce allergens, irritants, spores and toxins. They mainly affect the airways and lungs, and can also affect eyes and skin. Exposure is linked to asthma, rhinitis, bronchitis, respiratory infections, and symptoms like persistent cough and wheeze.

Official guidance from the Office for Health Improvement and Disparities, working with MHCLG and UKHSA, is blunt about the top of that range: the respiratory effects "can cause serious illness and, in the most severe cases, death."

Everyone is vulnerable. Greater risk falls on children, older people, pregnant women, anyone with a pre-existing respiratory condition, and anyone whose immune system is weakened.

If you or someone in the house has developed a persistent cough, worsening asthma or repeated chest infections while living with damp, see a GP and mention the housing conditions. But don't wait for that before reporting it. The guidance states plainly that landlords "should not delay action to await medical evidence or opinion", and that "medical evidence is not a requirement for action."

The blame question, settled

The standard response to a mould report is that you're drying washing indoors, not opening windows, or not heating the place properly.

Government guidance rejects that framing directly:

"It is totally unreasonable to blame damp and mould in the home on 'lifestyle choices'."

Understanding and addressing the health risks of damp and mould in the home

It goes on to identify the real causes as "building deficiencies, inadequate ventilation, inadequate heating and/or poor energy efficiency, not tenants' normal domestic activities."

And on the "just ventilate more" response: "Tenant management of condensation and small amounts of mould should not be a substitute for assessing and addressing the underlying issue, which should always be the priority."

That's worth quoting back, politely, if you're being told to buy a dehumidifier and stop cooking.

Working out what you've got

Three different problems, three different fixes.

Condensation

Looks like: black speckled mould, worst in corners, behind furniture on external walls, around window frames, on ceilings above showers. Often seasonal, arriving in October and easing in spring.

Caused by: warm moist air meeting cold surfaces. Which means cold surfaces are half the problem, so poor insulation, single glazing, no trickle vents and a broken extractor fan are all building faults.

Test: appears and worsens in cold weather, spread across several cold spots rather than one patch.

Penetrating damp

Looks like: a defined patch, often with a tide mark, sometimes with staining. Appears or worsens after rain.

Caused by: water getting in. Blocked or leaking gutters, cracked render, failed pointing, a slipped roof tile, a leaking pipe, a badly sealed window.

Test: is it in one place, and does it change with the weather rather than the season?

Rising damp

Looks like: a horizontal tide mark up to about a metre from the floor on a ground floor wall, sometimes with salt deposits and crumbling plaster.

Caused by: a failed or bridged damp proof course.

Test: ground floor only, and it doesn't go away in summer. Genuinely much rarer than the damp proofing industry suggests.

Where to look

Move furniture away from external walls and check behind it. Look inside wardrobes on outside walls, behind headboards, under sinks, in the corners of the ceiling in bathrooms, and around any window reveal.

The back of a wardrobe against a north-facing wall is where condensation mould is found most often and noticed last.

Treating it safely

Treat surface mould, but understand you're removing the symptom. Anything more than about a square metre, or anything recurring, needs the cause dealt with.

Do:

• Open a window and keep the room ventilated while you work.
• Wear rubber gloves, and a mask if there's more than a small patch. Goggles if you're working above head height.
• Use a proper fungicidal wash, following the instructions, or a mild detergent solution.
• Wipe rather than scrub, and dispose of the cloth afterwards in a sealed bag.
• Dry the area thoroughly afterwards.
• Wash affected soft furnishings at the highest temperature the label allows.

Don't:

• Brush or vacuum it dry. That flings spores into the air you're breathing. A regular vacuum won't hold them.
• Mix bleach with other cleaners. Bleach and ammonia produce a genuinely dangerous gas.
• Paint over it. Anti-mould paint on an untreated cause buys a few months and hides the evidence you'll need later.
• Ignore what's behind it. If plaster is soft or crumbling, the problem is deeper than the surface.

If anyone in the house has asthma or a weakened immune system, they shouldn't be doing this job or in the room while it's done.

Prevention that works when you can't change the building

None of this substitutes for fixing the cause, and it's worth saying so when you report the problem. But it does help while you wait.

• Use extractor fans and leave them running for fifteen minutes after a shower or cooking.
• Shut the door to the kitchen or bathroom while moisture is being produced, so it doesn't spread through the flat.
• Leave gaps behind furniture on external walls. A few centimetres genuinely makes a difference.
• Dry washing outside where you can. Where you can't, one room, door shut, window open or a dehumidifier running.
• Keep low background heat rather than short blasts. Cold surfaces are what condensation needs, and a house that swings between freezing and warm is worse than one held steadily mild.
• Don't block airbricks or trickle vents. Tempting in winter, and it makes things considerably worse.
• Wipe window condensation in the morning during cold months.

The heating point runs into a real problem, which is cost. If the property is expensive to heat, that's the building's fault and it's part of the case rather than an excuse. Our guides on getting a rented home ready for winter and what renting actually costs cover the practical side.

Reporting it properly

1. In writing, with photographs. Date them, and take more as it develops rather than one set.
2. Photograph the causes too, not just the mould. The broken fan, the painted-shut vents, the gap round the window, the gutter overflowing.
3. Describe the pattern. Which rooms, what time of year, whether it follows rain. That's what tells a surveyor which of the three you have.
4. Say who's in the house. Children, anyone with asthma or a respiratory condition, anyone pregnant. It changes the urgency and the guidance says it should.
5. Keep every reply. Especially any that blames your lifestyle, which is now demonstrably contrary to government guidance.

If nothing happens, your council's environmental health team can inspect and serve an improvement notice. It's free and it carries legal weight. What to do when a landlord won't repair and what to do if your home is unfit set out the routes.

What a proper repair looks like

Someone identifies the cause rather than the stain. That means checking for leaks, testing whether the extractor actually extracts rather than just makes a noise, looking at insulation and cold bridging, and checking gutters and pointing outside.

Then they fix that, treat the affected surfaces, and come back. Government guidance suggests inspecting again at least six weeks after remedial work to confirm it's actually resolved.

If all that happens is a coat of anti-mould paint, say so in writing at the time. When it returns in November you'll want the record showing they treated the symptom and never looked for the cause.

The bottom line

Damp and mould is a health matter and a building matter. Ventilate sensibly and clean small patches safely, but don't accept that as the answer, because official guidance doesn't either.

Report it in writing with photographs, name who's at risk in the household, and go to environmental health if you're ignored.

And if you spent a winter being told it was your washing, put it on the record. Reviewing your landlord and agent on Marks Out Of Tenancy is how the next family finds out before they move in.

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This guide covers England and reflects guidance current at August 2026. It is general information, not medical or legal advice: if you have health concerns, see a GP and mention your housing conditions. Sources: OHID, DHSC, MHCLG and UKHSA guidance on damp and mould, NHS.