Mayonnaise Left Out Overnight: Is It Safe?
Written by Jordan Morley · Reviewed against FSA chilling & danger-zone guidance · Last updated 28 October 2026
Opened mayonnaise left out overnight should be binned — once opened it's a refrigerated product, whatever its vinegary reputation.
Why overnight is too long
Opened mayonnaise is acidic, and USDA FoodKeeper notes that the fridge instructions on commercial jars are about quality rather than safety. On its own, a jar left out is lower risk than most perishable foods, but 'overnight' usually means 10 to 14 hours, past the 8-hour figure on the USDA's power-outage chart (above 10°C (50°F) for more than 8 hours means discard). The bigger risk is what mayonnaise is mixed into: potato salad, coleslaw, egg and tuna mayo and sandwiches are perishable and follow the 2-hour rule. Homemade mayonnaise is made with raw egg and no preservatives, so use the 2-hour rule for it too. Our verdict is to throw away a jar that has been open and out overnight.
You can also check the calorie content of mayonnaise alongside its safety information.
How long is too long? Three published limits against your overnight
Jar mayonnaise is acidic, so a jar left out is less risky than most perishable foods. But every published limit we found is shorter than a night, and the brand that makes the best-known jar sets the strictest:
| Limit | Who says it | Does overnight (roughly 10 to 14 hours) pass? |
|---|---|---|
| No longer than 4 hours out of the fridge | Hellmann's (US site): 'The general rule is no longer than four hours', and 'immediately refrigerate mayonnaise after opening' | No |
| Discard if above 50°F (10°C) for more than 8 hours | USDA / FoodSafety.gov chart for refrigerated food after a power cut: opened mayonnaise, tartar sauce, horseradish | No |
| 2 hours, or 1 hour above 90°F (32°C) | The general perishable-food rule from USDA, applied to mayo-based dishes | No |
Hellmann's also says the 'best by' date is mostly about quality, not safety, and that the jar should go in the fridge door and not freeze. Its US site does not give a room-temperature limit in its FAQ; the 4-hour figure is on its 'how long does mayo last' page. We found no UK Hellmann's statement, so the 4 hours is a US brand figure.
USDA FoodKeeper's own note says shelf-stable commercial mayonnaise is safe at room temperature after opening and that the fridge instruction on the label is about quality, not safety. So a jar alone is lower risk than almost any other perishable. We still say bin an opened jar left out overnight, because the brand's own limit is 4 hours, the USDA outage chart sets 8 hours, and an opened jar has had utensils in it (our reasoning, not a source's).
A worked example
You open a jar for dinner at 6pm, forget to put it away, and find it on the counter at 8am. That is 14 hours: more than three times Hellmann's 4 hours and nearly twice the USDA's 8-hour power-cut limit, and a room-temperature counter is far above the 50°F (10°C) threshold the USDA chart uses. Bin the jar.
What if it is mayonnaise in something?
| Item left out overnight | Verdict | Why |
|---|---|---|
| Opened jar of shop mayonnaise | Bin | Past every published limit above |
| Unopened jar | Fine | Unopened shop mayonnaise is shelf-stable; the refrigerate-after-opening advice applies once the seal is broken |
| Homemade mayonnaise or aioli | Bin, sooner than that in practice | Raw egg and no commercial acidity control: treat it as a 2-hour food |
| Potato salad, coleslaw, egg or tuna mayo, mayo sandwiches | Bin | The salad or filling, not the mayonnaise, is the perishable part; 2-hour rule |
| Single-serve sachet from a takeaway | No source we read gives a limit | Treat an opened sachet like an opened jar; an unopened one is fine |
Pregnant? The mayonnaise question is about eggs, not time
The NHS says mayonnaise made with raw egg is safe in pregnancy only if the eggs are British Lion or Laid in Britain eggs; other hen's eggs should be well cooked. Another UK chain, McDonald's, publishes that its mayonnaise and tartare sauce are made with pasteurised free-range egg; for any restaurant or takeaway, ask. That is a separate point from leaving a jar out overnight, which is a bin-it question for everyone.
Sources checked
Everything in the sections above was checked against these pages on 28 October 2026.
- Hellmann's (US): How long does mayo last? — 4-hour general rule; refrigerate immediately after opening; best-by is quality
- Hellmann's (US): FAQ — refrigerate after opening, fridge door, do not freeze
- USDA FSIS: Keeping Food Safe During an Emergency (refrigerated foods chart) — opened mayonnaise: discard if above 50°F (10°C) for more than 8 hours
- USDA FSIS: Leftovers and Food Safety — 2 hours, or 1 hour above 90°F, for perishable food
- USDA FoodKeeper — mayonnaise: fridge instructions are about quality
- NHS: Foods to avoid in pregnancy (page last reviewed 15 June 2026) — raw-egg mayonnaise safe only with British Lion or Laid in Britain eggs
- McDonald's UK: Can pregnant women eat your mayonnaise and tartare sauce? — McDonald's UK mayonnaise made with pasteurised free-range egg
Mayonnaise left out: which situation are you in?
| Situation | Verdict | Notes |
|---|---|---|
| Unopened jar, shop-bought | Fine | Shelf-stable until opened |
| Opened shop-bought jar, a few hours | Usually fine, but eat or chill | USDA power-outage chart: mayonnaise above 10°C (50°F) for over 8 hours is discarded |
| Opened jar overnight (10–14 hours) | Throw away | Beyond the 8-hour point on the USDA chart |
| Homemade mayonnaise | 2-hour rule | Raw egg and no preservatives |
| Potato salad, coleslaw, egg or tuna mayo, sandwiches | 2-hour rule | The other ingredients are the risk, not the mayo |
The 8-hour figure comes from the USDA's guidance on refrigerator power outages, not a general room-temperature rule. FoodKeeper itself notes that refrigerating opened commercial mayonnaise is about quality, but most people use the cautious 2-hour rule for mixed dishes.
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Mayonnaise: the other answers on this site
| Question | Short answer (links to the full page) |
|---|---|
| In pregnancy | Shop-bought is safe |
| In the fridge (Mayonnaise (Opened)) | 2 months in the fridge; 3–6 months in the cupboard |
| In the freezer | Not recommended |
Common questions
Is there an 8-hour rule for mayonnaise?
Not as a room-temperature rule. The 8-hour figure comes from the USDA's chart for refrigerator power outages, where mayonnaise above 10°C (50°F) for more than 8 hours should be discarded. Use it as an upper limit for an unopened-then-opened shop jar, not as permission, and overnight is usually longer than 8 hours.
Does homemade mayonnaise follow the same rule?
No. Homemade mayonnaise uses raw egg and has none of the preservatives or acidity control of a commercial jar, so use the standard 2-hour rule.
What if it's an unopened jar?
An unopened shop-bought jar is shelf-stable and fine out of the fridge. The label's fridge advice applies once it's open.
What about potato salad or coleslaw made with mayonnaise?
They follow the 2-hour rule (1 hour above about 32°C, such as at a summer picnic). The other ingredients, such as egg, potato, chicken and cooked pasta, are the main risk.
Does opened mayonnaise need the fridge?
The label usually says so. USDA FoodKeeper gives opened commercial mayonnaise about 2 months in the fridge, and notes that the fridge advice for shelf-stable commercial mayonnaise is about quality, not safety.
Is mayonnaise left out overnight dangerous or just unpleasant?
It can be either, and you cannot tell by looking. Hellmann's says no longer than four hours out of the fridge, and the USDA's chart says to discard opened mayonnaise held above 50°F (10°C) for more than eight hours. An overnight jar is past both.
Does mayonnaise really need to go in the fridge once opened?
Hellmann's says to refrigerate immediately after opening and keep the jar in the fridge door. USDA FoodKeeper notes that the fridge instruction on shelf-stable commercial mayonnaise is about quality rather than safety, so an opened jar is lower risk than most perishable foods. An opened jar left out all night is past the brand's 4-hour limit and the USDA's 8-hour chart, so we would still bin it.
Can pregnant women eat mayonnaise?
The NHS says mayonnaise made with raw egg is fine if it is made with British Lion or Laid in Britain eggs. For shop-bought jars that is normally the case, but check the label; for restaurant and takeaway mayonnaise or aioli, ask what egg they use.
Related answers
Primary source: FSA chilling & danger-zone guidance.
General information only, not medical advice: see the medical disclaimer. Feeling unwell after eating something? Contact NHS 111 or your GP.