I live in a flat with a flat above me and 2 below me, my walls in all the rooms tend to have what looks like damp patches but dont feel damp, i noticed in some areas in one bedroom the plaster was crumbing a bit and a day later white fluffy looking stuff started growing very fast, when touched it just disintegrates, does anybody know what this is? What causes it and is it harmful, i dont know wether it is connected but the room it grows in gets very cold all the time. Thanks in advance