Black mould on window frames is a clear sign that moisture is collecting around your windows. It looks unpleasant, can damage paint and sealant and may worsen allergies or asthma for some people. The key is to treat the mould safely and then reduce the moisture that causes it.
Why mould forms around windows
Window areas are prime spots for mould because they combine three things:
- Cold surfaces – glass and surrounding frames are often the coldest parts of the room.
- High moisture – condensation forms on the glass and can run onto seals and sills.
- Poor airflow – heavy curtains or blinds can trap still, humid air around the window.
Clean the mould safely first
Before changing anything else, remove existing mould so it cannot continue to spread. Always:
- Wear gloves and, if possible, a simple mask.
- Open a window for ventilation while you clean.
- Use a dedicated mould remover or a diluted bleach solution on hard, non porous surfaces.
Spray the affected areas, leave for the time recommended on the product and then wipe away with a disposable cloth. Avoid simply painting over mould, as it will usually come back through the new paint.
Reduce condensation on the windows
- Air the room each morning – open windows for five to ten minutes to let moist air escape.
- Keep trickle vents open if your windows have them.
- Avoid drying clothes in the same room where possible, or use a dehumidifier alongside the airer.
- Leave a small gap at the top of curtains so warm air can reach the glass.
Use a dehumidifier to keep humidity in check
A dehumidifier helps by reducing the overall amount of moisture in the room. When humidity is under control, there is less condensation on the glass and less water running down onto frames and seals.
For general use around the home, most people find a twenty litre model works well. You can see some strong options on our page covering the best dehumidifiers for UK homes.
When mould keeps returning
If mould returns quickly even after cleaning and reducing condensation, there may be other issues such as leaking gutters, damaged sealant or hidden damp in the wall. In those cases it is worth asking a professional to investigate so the source of moisture can be fixed properly.