How to Clean Windows & Remove Mold From Windowsill

Close-up of window with condensation and water droplets on glass, showing moisture buildup on cool surface.

We'll show you step-by-step directions for removing mold stains from windows and windowsills with the power of Clorox™ Disinfecting Bleach.

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Grime on windows is caused by buildup from dust, pollen, pollution, and moisture. Mold forms when condensation collects on windows, especially in humid or poorly ventilated areas. This moisture creates the perfect environment for mold spores to grow. Leaky seals or infrequent cleaning can make the problem worse.

How often should I clean windows?

Windows should be cleaned at least once a month, or more often in areas with high humidity or pollution. Regularly wipe down condensation and keep the area well-ventilated.

What does mold look like on windows?

Mold on windows often appears as black, green or gray spots along the glass, windowsills, or in the corners of the frame. It may look fuzzy, slimy or powdery, and often forms in areas where condensation or moisture builds up.

What should I use to remove mold on windows?

How to clean & get rid of mold on windowsills and frames with bleach

  1. Prep the area

    Remove any window treatments and nearby rugs. Place a towel under the window to protect the floor.

    Tip

    For better ventilation, open a nearby window or use a fan to help circulate fresh air.

  2. Pre-clean the surfaces

    If mold buildup is heavy, start by wiping the area with a wet microfiber cloth to reduce the amount of organic matter. Place the used cloth in the plastic bucket to wash later.

  3. Mix the bleach and water solution

    Wearing safety glasses and gloves, fill the spray bottle with 3 cups of water, then add 3 teaspoons of Clorox™ Disinfecting Bleach. Insert the spray nozzle and adjust it to a fine mist.

    Tip

    Make bleach and water solutions fresh each day as they lose potency over time.

  4. Apply the solution

    Hold a cotton washcloth under the area to catch drips, then spray the bleach solution onto the moldy areas. Keep surfaces wet for 10 minutes, spraying as needed. Use a microfiber cloth to wipe away mold and an old toothbrush for crevices.

    Tip

    Use multiple cloths, switching out dirty ones as you work to avoid spreading mold spores.

  5. Rinse the window

    Dampen a clean microfiber cloth with fresh water and wipe all treated areas to remove any leftover bleach solution.

  6. Dry the window

    Use a clean, dry microfiber cloth to thoroughly dry the window and prevent moisture buildup.

  7. Wash the cleaning cloths

    After finishing, wash all used microfiber cloths and washcloths on a hot, heavy-duty cycle with laundry detergent and 1/3 cup of Clorox™ Disinfecting Bleach.

Never mix bleach with ammonia, vinegar, or other cleaning agents, as this can produce hazardous gases.

How to remove mold and mildew from windowsills and frames with Clean-Up™ Cleaner + Bleach

  1. Preclean the area

    For visibly soiled surfaces, preclean before disinfecting.

  2. Spray surfaces

    Hold and spray Clorox™ Clean-Up™ Cleaner + Bleach 4–6 inches from surface until thoroughly wet.

  3. Wait

    Leave treated surface visibly wet for 5 minutes.

Do-it-yourself alternatives to clean windows

There are other do-it-yourself cleaning options but use with caution on surfaces due their acidic or abrasive qualities. Bleach is registered by the EPA to kill mold.

IngredientEffectiveness & Notes
BleachEPA-registered disinfectant for mold. Highly effective at killing mold on hard, nonporous surfaces when properly diluted.
Hydrogen Peroxide (3%)Not EPA-registered to kill mold. May reduce surface stains but not proven to eliminate mold spores.
White VinegarNot EPA-registered to kill mold. Can help clean and deodorize due to acidity. Use with caution.
Baking SodaNot EPA-registered to kill mold. Mild abrasive and deodorizer. May help clean surfaces but not kill mold.
Lemon JuiceNot EPA-registered to kill mold. Acidic properties may help with cleaning and odor, but not effective for killing mold.

Tips for how to clean windows with bleach

  • Know the right bleach-to-water ratio: https://www.clorox.com/learn/bleach-dilution-ratio/
  • Use freshly mixed solutions — bleach degrades over time when diluted.
  • Never mix bleach with vinegar, ammonia, or any other cleaner — it can create dangerous fumes.
  • Wear gloves and ensure good ventilation during use.

Frequently Asked Questions

Is mold on windows dangerous or harmful?

In small amounts, mold on windows is generally not harmful. However, heavy exposure may result in respiratory issues, allergies and other health problems, particularly for those with asthma or weakened immune systems. It's important to remove mold quickly and improve ventilation to prevent further growth.

Can mold grow on glass surfaces like windows?

Yes, mold can grow on windows, including the glass, especially when moisture and organic debris like dust are present. While glass itself isn’t porous, condensation and poor ventilation can create the damp conditions mold needs to grow on glass or around window frames and sills. Regular cleaning with a bleach solution can help eliminate mold.

What does mold look like on windows?

Mold on windows often appears as black, green or gray spots along the glass, windowsills, or in the corners of the frame. It may look fuzzy, slimy or powdery, and often forms in areas where condensation or moisture builds up.