What mildew is and where it grows

Mildew is a surface fungus that looks like a thin, powdery or slimy coating, usually gray, black, or white. Unlike mold, which grows deeper into porous materials, mildew stays on the surface of things—tile grout, shower walls, window sills, fabric, and painted wood. It thrives in damp, warm places with poor air circulation, which is why bathrooms, basements, and kitchens are common spots.

Mildew is easier to remove than mold because it hasn't penetrated the material. If you catch it early, a basic cleaning solution and a brush will usually do the job. The key is stopping it from coming back, which means controlling moisture in the space where it grew.

Key Takeaways

  • Mildew sits on surfaces and can be scrubbed away with a bleach solution, vinegar, or baking soda—no special equipment needed.
  • Bathrooms and basements need ventilation during and after showers or water use to prevent mildew from returning.
  • If mildew covers an area larger than 10 square feet or keeps returning after cleaning, the underlying moisture problem needs to be fixed first.
  • Porous materials like drywall or insulation that show mildew should be replaced, not cleaned, because the fungus has likely grown inside.

Cleaning mildew with bleach solution

The fastest way to kill mildew is a bleach and water solution. Mix one part household bleach (5 percent sodium hypochlorite) with three parts water in a spray bottle. Spray the affected area generously and let it sit for 10 to 15 minutes. The bleach kills the fungus on contact.

After the bleach has sat, scrub the area with a stiff brush or old toothbrush to remove the dead mildew. Rinse thoroughly with clean water and dry the surface completely with a cloth or towel. Open windows or run a fan to speed drying. Wear gloves and eye protection when using bleach, and never mix bleach with ammonia or other cleaners—the combination creates toxic fumes.

Bleach works best on non-porous surfaces like tile, glass, and painted wood. It can discolor or damage some fabrics and natural stone, so test it on a hidden area first.

Using vinegar or baking soda for gentler cleaning

If you prefer not to use bleach, white vinegar or baking soda will also kill mildew, though they work more slowly. Spray undiluted white vinegar directly on the mildew, let it sit for an hour, then scrub and rinse. Vinegar is safe around children and pets and won't damage most surfaces, but the smell is strong while it dries.

Baking soda works similarly: mix one teaspoon with one cup of water in a spray bottle, spray the mildew, wait 10 minutes, scrub, and rinse. You can also sprinkle dry baking soda on damp areas to absorb moisture and prevent mildew from starting. Baking soda is the gentlest option and safe for all surfaces, including fabric.

For stubborn mildew, make a paste of baking soda and water, explore it directly to the spot, let it dry, then scrub. This concentrates the cleaning power in one place.

Stopping mildew from coming back

Mildew returns when moisture lingers. In bathrooms, run the exhaust fan during and for 20 to 30 minutes after showers. If you don't have an exhaust fan, open a window and close the bathroom door to let moisture escape outside rather than spreading through the house. Wipe down shower walls and the tub after use to remove standing water.

In basements and other damp areas, use a dehumidifier to keep humidity below 50 percent. Check for leaks around pipes, windows, and foundation cracks—water seeping in will feed mildew no matter how often you clean. Fix any leaks promptly and seal cracks with caulk or hydraulic cement.

Improve air circulation by opening windows on dry days, running ceiling fans, and keeping furniture and boxes away from walls so air can flow behind them. In closets and under sinks, leave doors cracked open to prevent moisture from building up in enclosed spaces.

When to replace instead of clean

If mildew has grown on drywall, insulation, or wood framing, cleaning the surface won't solve the problem—the fungus has already spread into the material. These porous materials should be cut out and replaced. Mildew on drywall typically means water has been seeping in for weeks or months, and the wall cavity behind it may be affected too.

If mildew covers an area larger than 10 square feet, or if it keeps returning within a few weeks of cleaning, the underlying moisture source is too strong for surface cleaning to fix. In these cases, find and repair the water leak or ventilation problem before cleaning. Otherwise, the mildew will straightforward grow back.

Cleaning mildew from fabric and soft surfaces

Mildew on clothing, curtains, or upholstery can often be removed by washing in hot water with detergent and a cup of white vinegar or baking soda. Dry the item completely in direct sunlight if possible—UV light kills mildew spores. For delicate fabrics, soak in a baking soda solution instead of using bleach.

If the fabric still smells musty after washing, soak it again in vinegar solution, rinse, and dry in the sun. If mildew has caused permanent staining or the smell won't come out, the item may need to be discarded. Prevent mildew on stored clothing by keeping closets and storage areas dry and well-ventilated, and never storing damp items.

Frequently Asked Questions

Is mildew dangerous to breathe?

Mildew spores can irritate airways and trigger allergies or asthma in sensitive people, especially in poorly ventilated spaces. It is not as serious as some molds, but removing it and controlling moisture will improve indoor air quality. If someone in your home has respiratory issues, cleaning mildew promptly is worth the effort.

Can I use bleach on bathroom tile grout?

Yes, bleach is safe and effective on grout. Spray the bleach solution directly into the grout lines, let it sit 10 to 15 minutes, then scrub with a grout brush or old toothbrush. Rinse thoroughly. For stubborn stains, you can let bleach sit longer, but always ventilate well and wear gloves.

Why does mildew come back so fast in my shower?

Showers are the perfect environment for mildew—warm, wet, and often poorly ventilated. Run your exhaust fan during and after every shower, wipe down walls and the tub, and leave the shower door or curtain open to dry. If mildew returns within days, your exhaust fan may not be working properly or may be venting into the attic instead of outside.

Can I prevent mildew with a spray or coating?

Mildew-resistant coatings and sprays exist, but they work only if you also control moisture. No coating will stop mildew if the area stays damp. Focus first on ventilation and drying, then use a preventive spray if you want an extra layer of protection.