Mould on windows is a common issue for many homeowners, particularly in areas with high humidity or poor ventilation. Not only is mould unsightly, but it can also pose health risks if left untreated. Mould growth on windows is primarily caused by excess moisture. This can result from condensation, leaks, or high humidity levels. How to prevent it? You can improve the ventilation, by using exhaust fans in kitchen and bathroom to reduce the humidity. Also open windows regularly to promote airflow. Check for and repair any leaks around windows to prevent water from seeping in. Proper insulation of windows can reduce condensation by maintaining a consistent door temperature.