Mold is notoriously prolific, and certain types have been identified as toxic to human health for hundreds of years. Mold proliferates through microscopic airborne spores, which act similarly to seeds. If a mold spore lands on a wet surface, it can grow and release more spores, spreading quickly and can potentially be catastrophic to health. There are many variations of mold, but none of them will grow without moisture.
In some instances, basic molds that are caught early can be removed by the homeowner. However, professional inspection and judgment may be necessary in certain instances, such as if there are immune-compromised individuals present. In most cases, it is impossible to completely sterilize an area, as nature has created mold to be so resilient that no matter what some level of trace spores will remain, however they will not grow if the moisture has been resolved.