Commercially prepared mayonnaise is generally made with acidic ingredients that help limit the growth of certain harmful bacteria. However, that doesn’t mean it should be left unrefrigerated indefinitely. Once opened, mayonnaise should be kept sealed and refrigerated according to the manufacturer’s instructions. Homemade mayonnaise, particularly when made with raw eggs, can carry additional risks and requires careful preparation and storage.

The bigger concern often involves the foods mixed with mayonnaise. Chicken, potatoes, eggs, and other prepared ingredients can become unsafe when left at room temperature for too long. Bacteria such as Salmonella and Staphylococcus aureus may multiply when food is improperly handled or stored. As a general food safety rule, refrigerate perishable dishes within two hours, or within one hour when temperatures exceed 90°F (32°C).

Cross-contamination is another common problem. Using a spoon that has touched other foods and then returning it to the mayonnaise jar can introduce unwanted microorganisms. Clean utensils, proper refrigeration, and good kitchen hygiene help reduce this risk. At outdoor gatherings, keep cold dishes chilled in a cooler or over ice, and return leftovers to the refrigerator promptly rather than leaving them on the table throughout the afternoon.

Mayonnaise often gets blamed when someone becomes ill after a picnic, but the actual cause may be contaminated ingredients or improper storage of the finished dish. This doesn’t mean mayonnaise-based foods are risk-free; they still require the same sensible precautions as other perishable meals. With clean utensils, appropriate refrigeration, and careful food handling, mayonnaise can remain an enjoyable part of everyday cooking and outdoor gatherings.

The important lesson is that food safety depends on the entire dish and how it’s handled—not simply on whether it contains mayonnaise.