Refrigerate or Leave Out? The Truth About Mayonnaise Storage

Mayonnaise is a common kitchen staple, used both as a condiment and as an ingredient in many recipes. Yet one question continues to cause confusion: does mayonnaise need to be refrigerated, or can it safely sit out? The answer matters, because improper storage can increase the risk of foodborne illness and shorten shelf life.

The science behind mayonnaise

Mayonnaise is an emulsion made from oil, egg yolks, and an acid such as vinegar or lemon juice. The egg yolks contain lecithin, which allows the oil and liquid to stay blended. The acidic component helps slow bacterial growth, but it does not eliminate risk entirely.

Commercially produced mayonnaise is made with pasteurized eggs and often includes preservatives. These factors significantly improve its stability and safety compared to homemade versions. Homemade mayonnaise, which typically uses raw egg yolks and no preservatives, is far more vulnerable to spoilage.

Refrigeration: when it’s necessary

Store-bought mayonnaise: Once opened, it should always be kept refrigerated. Even though it contains acid and preservatives, leaving it at room temperature for extended periods can still allow harmful bacteria to grow.
Homemade mayonnaise: This should be refrigerated at all times and used within a short window, usually 3–5 days.

Leaving mayonnaise out during a meal—such as on a table or buffet—is generally safe for a short period, but it should not be left unrefrigerated for hours. Warm temperatures accelerate bacterial growth, especially once the jar has been opened.

Why proper storage matters

While mayonnaise has a reputation for causing food poisoning, illness is more often linked to cross-contamination—such as using the same utensil for raw foods and then dipping it back into the jar—or prolonged exposure to warm temperatures.