Older windows are bound to leak and that means both air and water. If your windows have let water in after a rainstorm and you didn’t notice at first, you’ll want to get rid of the mold that forms as quickly as you can. The mold will only spread if you ignore it.
To clean mold, get dish soap, water, bleach, a dry cloth, a plastic scrubber, cleaning gloves, eye goggles, and a protective face mask so you don’t breathe the spores in. Mist the mold with a spray bottle so you weigh down the spores before you start scraping them off. Then, mix soap with water and apply it to the windowsills. The mold will start to loosen, and you can continue the process with the scrub brush. After the mold is gone, mix bleach with water and let it sit for 15 minutes in the places that are affected. Then, rinse the window sills with clean water and dry them thoroughly. Leave the windows open for a while to let the drying complete.