This is caused by a build up of moisture inside the property and it being warmer in side than it is outside.
You need to wipe down the moisture from the windows –especially in the winter months when you have the heating on and it is cold outside. Moisture can be caused by showering, cooking, drying clothes inside and even breathing.
Too much build up of moisture in the property will result in mould spores beginning to form on the walls, ceilings, behind furniture and around the windows.
You must ventilate each of the rooms as and when you are showering, cooking and drying any clothes inside. Please keep the ventilation until the moisture has gone from the room.
It is vital to use the heating for a small period of time each day, mainly in the winter, to keep the heating levels moderate in the property.
Any affected areas can be wiped down regularly using a sponge and diluted bleach. You can also use black mould remover spray, leave for a few hours and then wipe away.
Do not leave mould spores to spread further, at the first sighting please remove using your chosen method of cleaning product.
Review guide to understanding damp and mould can be found here: