Mould is eukaryotic micro-organisms that exists anywhere there is water, warm climate, and a food source. Mould consumes material like drywall and wood. In our modern day times people generally construct their buildings out of drywall and other wood based products which can result in a number of problems in which mold may arise in the home itself. Mould will grow in damp locations like a basement or a bathroom. Mould spores are harmful to inhale, especially for people with asthma or who are sensitive to allergies. Thousands of different strains exist but only a handful can be found in any one home.
Mould can be cleaned from the surface, but because mould spores are in the air and on surfaces we can’t see, the mould will grow back. To prevent this from happening, you must eliminate the source of the mould problem. Where did the water damage come from? How is water accumulating on the ceiling? Is the basement flooding? Once you clean up and resolve the water issue, you need to supply ventilation to those particular rooms and if you can, purify/filter the indoor air or replace your indoor air with fresh outside air. This will reduce the mould greatly and reduce the chances of mould re-appearing. If you are still worried or you still smell the musky odour, you can have a professional test the air for mould.