Mayonnaise is a common kitchen staple, but storing it properly is important for keeping it fresh and safe. It is made with oil, egg yolks, and an acid such as vinegar or lemon juice. Commercial mayonnaise often contains pasteurized eggs and preservatives, while homemade versions usually spoil faster.

Once opened, mayonnaise should always be refrigerated. The USDA recommends keeping perishable foods below 40°F (4°C) and not leaving them at room temperature for more than two hours. In temperatures above 90°F (32°C), that limit drops to just one hour. Refrigeration helps slow bacterial growth while preserving the mayonnaise’s taste and texture.

Leaving mayonnaise out too long can increase the risk of foodborne illnesses, including those caused by Salmonella and Listeria. Spoiled mayonnaise may have a bad or rancid smell, unusual color, changed texture, separation, or visible mold. If you notice any of these signs, it should be thrown away rather than tasted.

Individual shelf-stable mayonnaise packets are different because they are designed to remain at room temperature until opened. However, once opened, they should be treated like regular mayonnaise and refrigerated when necessary.

For the safest option, put mayonnaise back in the refrigerator promptly after using it. If it has been sitting out beyond the recommended time, it is better to discard it than risk getting sick. As the original article states, “Refrigeration slows bacterial growth and helps preserve the mayonnaise’s texture, flavor, and quality.”