Whenever possible, use a paper towel or a clean dishcloth instead to wipe up. If you do use a sponge, sanitize it regularly. Lisa Yakas, a microbiologist at NSF International, a public health and safety organization that develops standards and certifications, recommended several methods. Dampen your sponge and microwave it for 2 minutes; run it through a dishwasher on a setting that reaches at least 155 degrees and use the heated drying cycle; or submerge your sponge in a bleach solution (3/4 cup bleach to 1 gallon of water) for at least 5 minutes and then rinse thoroughly. We've found that sponges can burn in a high-powered microwave, so we prefer to use the dishwasher or the bleach solution method. After using any of these techniques, allow the sponge to dry completely before using it again, ideally in a dish rack or a container that allows air to circulate around all surfaces of the sponge. Yakas also recommended replacing your sponge regularly, every 1 or 2 weeks.
To find the best method, we tried microwaving, freezing, bleaching, and boiling sponges that had seen a hard month of use in the test kitchen, as well as running them through the dishwasher and simply washing them in soap and water. Lab results showed that microwaving and boiling were most effective, but sponges can burn in a high-powered microwave, so we recommend boiling them for 5 minutes.