Mold causes mildew to form on and around window sills from excessive moisture within the home. Moisture condenses on window glass, especially when the outside temperature is cold and the inside temperature is warm. The moisture runs down the window and collects on the window sill. When liquid remains on the window sill, mould spores form and spread. Mold left unattended can cause health and breathing problems.
Vacuum any mould growing on or around windows using a sweeper attachment or a hand-held vacuum. Remove the sweeper bag containing the mould spores and deposit the bag in an outside dustbin.
Put on a pair of rubber gloves. Fill a bucket with warm water and two squirts of dish detergent. Using a sponge, wipe the soapy solution on the mould around the windows. Rinse the soap from the window sills with clean water and a damp rag.
Mix a solution of 2 tablespoons liquid chlorine bleach and 1 quart of warm water in a bucket. Apply the bleach solution around the window sills. The bleach kills and removes any leftover mould spores. Allow the bleach mixture to remain on the surface of the window sill for 10 minutes before removing.
Wipe the bleach solution from the window sills with a damp rag. Dry around the windows with a clean cloth.
Wipe windows and window sills with a clean rag whenever you see moisture forming. Run a dehumidifier in the house to remove excess moisture. Open windows during dry months to let in fresh air. Keep windows closed during periods of high humidity.