Bleach kills cooler mold.

Yes, and it’s simple. Scrub out loose gunk with dish soap and water, then mix 1 tablespoon bleach per quart of water (or 1/4 cup per gallon). Swish that around, let it sit for 15 minutes, then rinse thoroughly. Let the cooler air dry completely with the lid open before storing again.

Bleach is the reliable option here. Vinegar can help with surface mildew, but for black mold that’s been festering in a damp cooler, bleach actually kills the spores. Don’t skip the rinse — you don’t want bleach residue next to your sandwiches.

After cleaning, leave the lid propped open for a day or two. Storing it dry is the whole trick. If the mold smell lingers, a baking soda paste scrub after the bleach step helps with odors.

Next time, toss a crumpled paper towel or a small desiccant pack in there before sealing it up. Mold needs moisture, and you just took that away.