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How to get rid of mould on window frames safely

Rive News Research Desk

Published October 16, 2026 · 8 min read

Key takeaways

Mould on window frames grows where condensation keeps frames damp, so cleaning alone will not stop it returning.
Never dry-brush mould, and wear gloves and a mask, because scrubbing dry growth spreads spores through the air.
A fungicidal wash made for mould beats plain bleach, and drying the frame after cleaning matters as much as the wash.

A handprint in condensation on a window panePhotograph: PexelsImage: Pexels

Black spots creep along the bottom of a window frame. You wipe them away, and a few weeks later they are back. That cycle is normal, because the mould is a symptom.

The cause is moisture, and window frames are where indoor moisture shows up first.

This article explains how to clean mould off window frames safely, what never to do, and how to cut the condensation that feeds regrowth.

Why window frames grow mould

Mould needs three things: moisture, a surface to grow on, and time. Window frames supply all three in cold months. Warm, moist indoor air hits cold glass and cools, and the water in it condenses into droplets on the glass and frame.

Those droplets sit on the frame, soak into sealant and paint, and give mould spores a damp home.

Condensation is the most common cause of damp and mould in homes, according to Manchester University NHS Foundation Trust. The Trust notes that almost 1 in 3 homes in England have damp and mould, and that it is more common in rented homes. Cooking, showering, drying clothes indoors, and even breathing all add moisture to indoor air.

When windows stay shut and heating stays low, that moisture has nowhere to go except onto cold surfaces.

The frame material matters too. Sealant and the corners where glass meets frame trap water. Dust in window tracks holds moisture.

Failed seals let water in from outside. A frame that stays wet for days will grow mould even in a clean house, because spores are always present in indoor air, waiting for a damp spot.

What mould does to health

Moulds produce allergens, substances that can cause an allergic reaction, along with irritants and sometimes toxic substances. Inhaling or touching mould spores may cause sneezing, a runny nose, red eyes, and a skin rash. Moulds can also cause respiratory problems and infections, and can trigger asthma attacks, according to NHS guidance published by Spring Hill Practice.

Some people are more sensitive than others. Babies and children, elderly people, people with existing skin problems such as eczema, people with respiratory problems such as allergies and asthma, and people with a weakened immune system should stay away from damp and mould. If anyone in the home has asthma that keeps flaring, mould near windows is worth treating as a suspect, not just a stain.

Size matters as well. Small surface patches on a frame are usually a cleaning job. Guidance cited by Rainbow Restoration advises that if mould covers an area larger than one square metre, or has soaked into plaster or wallpaper, a professional mould removal company should handle it.

Do not try to scrub a large or deep infestation yourself, and speak to your landlord first if you rent, since structural damp is their repair to make.

What you need before you start

Gather everything before you touch the mould. You will need rubber gloves, a face mask, a spray bottle, a specialist mould spray or fungicidal wash, a soft cloth or sponge, a soft brush or old toothbrush for corners, and a bin bag for used cloths. Open the window and, if you can, open a door to create airflow through the room.

Wear the gloves and mask for the whole job. Mould spores irritate skin and airways, and cleaning stirs them up. Keep children, pets, and anyone with asthma or allergies out of the room while you work.

If you are pregnant, have asthma, or have a weakened immune system, ask someone else to do the cleaning.

Pick your cleaner with care. There is honest disagreement in published guidance here. Some NHS advice says to wipe mould off hard surfaces with a damp cloth using soapy water or a diluted bleach solution, then dry the area thoroughly.

Other NHS practice guidance says bleach and washing-up liquid do not kill mould effectively, and recommends a specialist mould spray that carries a Health and Safety Executive approved number. For window frames, the specialist fungicidal wash is the better pick, because it is made to kill mould and to keep working on the surface. Whatever you use, follow the maker's instructions and never mix bleach with other cleaners.

The safe cleaning method, step by step

Ventilate the room. Open the window and let fresh air move through. Do not use a fan that blows across the mould toward you.
Wet the mould first. Spray the cleaner onto the growth so the surface is damp. Never scrub mould while it is dry, because dry brushing releases large numbers of spores into the air.
Let the cleaner sit. Leave it for the time the label states, usually 10 to 20 minutes, so it can kill the growth instead of just moving it around.
Wipe, do not scour. Use a soft cloth or sponge to lift the mould, working from the edges inward. Use a soft brush or old toothbrush for corners and sealant grooves, with light pressure that will not scratch the frame.
Rinse and dry. Wipe the area with a clean damp cloth, then dry it fully with a fresh cloth. Moisture left behind invites the mould back within days.
Bag the waste. Put used cloths and sponges in a bin bag, tie it, and take it to an outside bin. Wash your gloves and hands after you finish, and wash any cloths you plan to reuse in hot water.

Check the frame after cleaning. If the sealant itself is black deep inside, or the frame paint is soft and peeling, the mould may have grown into the material. Cleaning the surface will not fix that.

Sealant with deep growth should be cut out and replaced, and rotted timber needs repair, because mould keeps returning to damaged material.

A woman wearing an apron cleaning a glass windowPhotograph: Antonius Ferret / PexelsImage: Pexels

What never to do

Never dry-brush, scrape, or vacuum mould. Dry methods launch spores into the air and spread the problem to other rooms. NHS guidance warns against disturbing mould by brushing or vacuuming, because it can raise the risk of breathing problems.

Never mix bleach with vinegar, ammonia, or other cleaners. Mixing cleaners can release gases that burn the eyes and lungs. If you choose a bleach-based product, use it alone, in a ventilated room, and keep it away from fabrics and coloured frames that it can stain.

Never paint over mould. Paint seals the growth in but does not kill it, and mould keeps growing under the new coat. Clean and dry the area first, and use a fungicidal paint only after the surface is fully clean and dry, if you redecorate at all.

Never ignore a patch that keeps returning in the same spot. Repeat growth points to a moisture source that cleaning cannot fix: a leaking seal, a blocked window drain hole, or condensation that never dries. Find the water before you clean again.

How to stop it coming back

Prevention beats cleaning, because mould returns whenever frames stay damp. The single most effective habit is wiping condensation off windows each morning. Heath Showman of Lifestyle Blinds, quoted in the Glasgow Times, recommends a microfibre cloth or squeegee for the job, and wringing the cloth out over a sink or outside the room rather than near the window.

Clean the glass, the sills, and the frame edges, where moisture collects and causes the most harm.

Ventilation comes next. Open windows briefly each day, especially after cooking or showering, and keep trickle vents open where your windows have them. Run extractor fans in kitchens and bathrooms, and close internal doors while steam builds so damp air does not drift to cold bedrooms.

Cover pans while cooking, and dry clothes outside or in a ventilated room when you can.

Heating helps too. A home kept steadily warm has warmer glass and frames, so less moisture condenses on them. If you can afford it, avoid letting rooms go cold for long stretches in winter.

Move furniture slightly away from external walls so air can circulate behind it, and clear dust from window tracks and drain holes so water can escape instead of pooling.

Check the frame itself once a year. Look for cracked sealant, failed double-glazing seals that fog between panes, and paint that has lifted. Fixing a seal costs far less than fighting mould on a rotting frame.

If you rent and the problem is structural, report it in writing to your landlord, since repairs to leaks, seals, and insulation are normally their responsibility. While you wait, keep up the wiping and ventilation routine, which slows regrowth even when the root cause is not yet fixed.

The bottom line

Mould on window frames is a moisture problem with a cleaning step, not a cleaning problem on its own. Clean it wet, with gloves and a mask, using a fungicidal wash, and dry the frame after. Then attack the cause: wipe condensation daily, ventilate after cooking and showering, and fix seals that let water in.

If the patch is large, deep, or tied to structural damp, get professional help instead of scrubbing harder. For other small household fixes, see how to replace a tap washer to stop a dripping tap or unblock a kitchen sink with a plunger.

Tags: mould, windows, condensation, cleaning

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