Other gentle alternatives to bleach include full-strength white vinegar or a tea-tree oil solution. “Tea tree oil is my favorite mold-killer because it’s such a broad-spectrum fungicide,” says Annie Berthold-Bond.

Ms. Berthold-Bond mixes two teaspoons of tea-tree oil and two cups of water in a spray bottle, and then applies it directly to the surface, with no rinsing. Its very strong odor lingers for a few days, she told Well Journal, but “I’ve never had a mold problem that tea tree oil hasn’t killed.” Take care when using essential oils, Ms. Berthold-Bond cautions, especially if you have allergies. “Keep them away from your eyes and skin,” she says, and test your tolerance before applying to a large area of a room.