Mayonnaise Left Out Overnight: Is It Safe?
Reviewed against FSA chilling & danger-zone guidance · Updated September 2026
Nutritional data sourced from USDA FoodData Central and Public Health England. Always consult a registered dietitian for personal dietary advice.
Opened mayonnaise left out overnight should be binned — once opened it's a refrigerated product, whatever its vinegary reputation.
Why overnight is too long
Commercial mayonnaise is actually more forgiving than most perishable foods — the USDA's specific guidance for opened, shop-bought mayonnaise is up to 8 hours at room temperature, not the standard 2-hour rule, thanks to its vinegar and preservatives. The catch is that 'overnight' almost always runs longer than 8 hours (an evening meal left out until morning is typically 10-14 hours), which pushes it past even this more generous window. Homemade mayonnaise is a different matter — made with raw, unpasteurised egg and no preservatives, it should be treated with the standard 2-hour rule instead.
You can also check the calorie content of mayonnaise alongside its safety information.
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Common questions
Is there really an 8-hour rule for mayonnaise, not 2 hours?
Yes — for opened commercial mayonnaise specifically, the USDA's own guidance allows up to 8 hours at room temperature, longer than most perishable foods. It doesn't help with an overnight window though, since that's usually well past 8 hours.
Does homemade mayonnaise follow the same rule?
No — homemade mayonnaise uses raw egg with none of the preservatives or acidity control of a commercial jar, so it should follow the standard 2-hour rule, not the 8-hour one.
What if it's an unopened jar?
An unopened, shop-bought jar of mayonnaise is shelf-stable and doesn't need refrigeration at all until opened — a sealed jar left out overnight is not a safety concern.
Related answers
Primary source: FSA chilling & danger-zone guidance.
The information on 247foodcheck.com is compiled from official public guidance (NHS, Food Standards Agency, USDA/FDA FoodKeeper) and is provided for general information only. It is not medical advice and does not replace guidance from your midwife, GP, health visitor or other qualified professional. When in doubt, throw it out — and if you feel unwell after eating something, contact NHS 111 or your doctor.