Mayonnaise is a perishable food item that contains eggs and other ingredients that can spoil quickly when left at room temperature. The general rule for mayonnaise is that it should not be left out of the fridge for more than 2 hours.
Bacteria can multiply rapidly in mayonnaise when it is exposed to temperatures between 40°F (4°C) and 140°F (60°C), which is known as the "danger zone" for food safety. Leaving mayonnaise in this temperature range for an extended period can lead to the growth of harmful bacteria and cause foodborne illnesses.
To ensure the safety and quality of mayonnaise, it's best to refrigerate it promptly after use. If you're hosting a gathering or a picnic and plan to have mayonnaise-based dishes, try to keep them in a cooler with ice packs to maintain a safe temperature. When in doubt, discard any mayonnaise that has been left out at room temperature for more than 2 hours.