Difference between molds and mildew allergies?

None: Mildew is one of several manifestations of molds.

Allergies: Mildew is white, mold black or other colors. Both smell bad. Mold grows on paper, wood, other fibers. People with allergies (runny nose, irritated eyes, asthma) may have severe symptoms related to exposure to the substance(s) to which they are allergic. People differ. See Wiki article https://en.wikipedia.org/wiki/Mildew