Mould is a fungus and, as typical in these tiny organisms, you may observe it growing in humid corners despite your careful regular cleaning and maintenance of your house. As you might already know, it can cause a lot of damage to the walls and furniture, but worse than that, it can cause breathing and skin problems if you are in contact with it regularly. For these reasons, you should be mindful and try to prevent mould appearing in your house in the first place.