Wherever there are the right conditions, including warm air, moisture and something on which to cling, mold will continue to grow and grow. If it is not stopped it can quickly destroy an entire house. Mold is very dangerous.
Mold is a fungus. A fungus is in many ways like a plant, but is really an organism all to itself. Instead of producing seeds, it produces spores, which are generally sent through the air to surrounding fertile habitations.
The expressions of mold - mold odors - can contain some very dangerous components that can and will cause respiratory infections that require horribly invasive treatment. Mold smells are light a 'check engine light' a warning sign that must be heeded.
Mildew is within the same class of organism as mold, but has a shallower root system. Where mold has a veracious appetite, growing directly on its food-source (breads, rotting vegetables, soaked surfaces full of yummy bacteria), mildew can survive with less. It will grow and begin showing its black dots (instead of spots) on surfaces like lightly dampened paper, ceramic tile grout, clothing materials, etc.
The very fact that you can see mildew is indicative that there is trouble a-lurking. The surfaces on which mildew grows are not generally perceived to be vigorous food sources for even the tiniest of fungus, and may not emit any noticeable mildew smells or odors; however, what it should be telling you is that there is, behind the mildew, colonies of bacteria that are growing and feeding the fungus. Get rid of the mildew, be rid of the bacteria.