Mildew is a black mold that lives in warm, moist areas, such as bathrooms and showers. Mildew is unsightly, causing a musty odor and, if untreated, will leave permanent stains. Hydrogen peroxide, however, will remove mildew from a fiberglass shower.
Mildew requires warm, moist conditions and often begins to take root in cracks, crevices and corners in the shower. Check for black spots around the drain and faucet, in the caulk around the seams of the shower, and in any other areas where water may collect and sit.
Pour 3 percent hydrogen peroxide directly on the affected areas of the shower, then wipe clean with a damp rag or sponge. Scrub gently, if necessary, to remove all visible mildew. For stubborn stains, soak a cotton ball or paper towel in hydrogen peroxide and let it sit on the mildew stains for several minutes to break up the mildew.
Because mildew needs moisture to survive, preventing mildew requires eliminating all excess moisture in the bathroom. Use a towel to wipe the shower after each use. Use an exhaust fan or dehumidifier to remove moisture from the air. Frequently cleaning the shower can remove mildew spores before they take root.