My nana always stores mayonnaise on the counter instead of the fridge. I'm nervous about eating it after a few days. How long can mayonnaise stay out safely?

How Long Can It Safely Stay Out?

According to official food safety guidelines from the USDA and the FDA, the rules are definitive:

The 2-Hour Rule: Once a jar of opened mayonnaise drops below refrigerator temperatures and enters the "danger zone" (40∘F to 140∘F or 4∘C to 60∘C), it should not be left out for more than 2 hours. If the kitchen hits a warm 90∘F (32∘C) or higher, that window drops to just 1 hour.

If a jar has been sitting on the counter for days, the official advice is clear: throw it out. While the acidity of the mayo might prevent you from getting severely ill every single time, you are rolling the dice on cross-contamination.

A Simple Compromise

If you love your nana but value peace of mind, you don't have to start a family feud. The easiest fix is switching her over to a squeeze bottle of mayonnaise.

Because a squeeze bottle never requires a knife or spoon to go inside, the risk of cross-contamination drops to almost zero. While the USDA still recommends refrigerating it after opening to maintain its fresh taste and prevent the oil from separating, a squeeze bottle left on the counter is vastly safer than a jar full of stray breadcrumbs