The Cause

Musty odors: The thick stench that seeps into books, quilts, and maps of the countries you backpacked through in college is caused by moisture that gets trapped in unventilated spaces, resulting in mold and mildew that breed odor-causing bacteria.
Water damage: Water damage can cause leaks, and leaks create odors that won't dissipate until the wet spots — and the source of the damage — are dry.

The Cure

Musty odors: "Activated charcoal reduces odors," says Meredith Montague of Boston's Museum of Fine Arts. Pour two cups into an airtight bin, prop your items on a showbox in the bin so they don't touch the powder, seal until fresh, then air them out.
Water damage: Once the source is sealed, ventilate and turn on a dehumidifier, like the Kenmore 50-pint model ($180, www.sears.com).