How Long Mayonnaise Stays Safe at Room Temperature

Mayonnaise should not sit out for more than two hours at room temperature

Mayonnaise is an emulsion—a blend of oil, egg yolk, and acid held together by the egg's natural lecithin. That structure makes it stable in the refrigerator, but unstable on the counter. The real risk is not the mayo itself, but the raw egg yolk it contains. Salmonella bacteria can live in raw eggs, and they multiply fastest between 40°F and 140°F—the "danger zone" where your kitchen counter sits.

The U.S. Food and Drug Administration (FDA) and the USDA both set the limit at two hours for any food containing raw eggs left at room temperature. If your kitchen is warmer than 90°F, that window shrinks to one hour. Once mayo has been left out past that point, the safest choice is to throw it away. You cannot see, smell, or taste Salmonella, so there is no way to know if it has grown to unsafe levels.

This applies to homemade mayo and store-bought mayo alike. Commercial mayo is acidified (vinegar or lemon juice is added), which slows bacterial growth, but it does not stop it completely. The two-hour rule still holds.

Key Takeaways

• Mayonnaise left out at room temperature for more than two hours should be discarded, because raw egg yolk in mayo can harbor Salmonella that multiplies in the danger zone.
• If the room temperature is above 90°F, reduce the safe window to one hour.
• Store-bought mayo is more acidic than homemade, which slows bacterial growth slightly, but both types follow the same two-hour rule.
• You cannot detect Salmonella by sight, smell, or taste, so timing is your only reliable safety measure.
• Once mayo has been left out past the time limit, throwing it away is the only safe option—there is no way to salvage it.

Why the Two-Hour Rule Matters for Mayo Specifically

Mayonnaise is a high-risk food for bacterial growth because it combines two things: raw egg and an environment where bacteria thrive. The egg yolk is the culprit. Even though mayo is acidic, that acidity does not kill existing Salmonella—it only slows new bacteria from multiplying. If Salmonella was present in the egg before the mayo was made, it can still grow once the jar is opened and left out.

The danger zone (40°F to 140°F) is where Salmonella doubles in number every 20 minutes under ideal conditions. After two hours at room temperature, the bacterial count can reach levels that cause food poisoning. Symptoms—nausea, vomiting, diarrhea, fever—usually appear 6 to 72 hours after eating contaminated food and can last a week or longer.

Refrigeration slows this process almost to a stop. At 40°F or below, Salmonella growth is so slow that mayo can safely last for months in the fridge. That is why the refrigerator is the only safe storage place for mayo once it has been opened.

How to Handle Mayo at Picnics and Outdoor Events

Picnics, barbecues, and potlucks are where mayo-based foods most often get left out too long. Potato salad, coleslaw, and sandwiches with mayo all carry the same two-hour limit. If you are bringing a mayo-based dish to an outdoor event, keep it in a cooler with ice packs until serving time, and return it to the cooler as soon as the meal is over.

If you are unsure how long a mayo dish has been sitting out, do not eat it. The cost of throwing away one serving is far lower than the cost of food poisoning. At outdoor events, it is common for dishes to sit out longer than intended, especially if people are eating over several hours. When in doubt, assume the two-hour window has passed.

For events lasting more than two hours, bring mayo-based dishes in a cooler and only set out small portions at a time, refreshing them from the cooler every two hours. This keeps the bulk of the food safe while still allowing guests to eat when they want.

Opened vs. Unopened Mayonnaise Storage

An unopened jar of mayo can sit in the pantry at room temperature for months, sometimes a year or longer, depending on the brand and storage conditions. The seal keeps air and bacteria out, and the acidity preserves the product. Check the expiration date on the jar—that is your guide for unopened mayo.

Once you open the jar, the two-hour rule kicks in immediately. The moment air enters the jar, the protective seal is broken. Any mayo that has been exposed to room temperature for two hours or more should be discarded, even if the jar is not yet expired. After opening, always refrigerate the jar between uses, and always use a clean spoon or knife to scoop mayo out—never double-dip or use a utensil that has touched other foods.

Opened mayo stored in the refrigerator typically lasts 2 to 3 months, though some sources say up to 6 months if stored properly. The jar should be sealed tightly after each use, and the lid and rim should be wiped clean to prevent mold growth. If you see mold, discoloration, or smell anything off, throw the jar away.

Signs That Mayo Has Gone Bad

Mayonnaise can spoil in ways you can see and smell, even though Salmonella contamination is invisible. Look for mold on the surface or inside the jar—this is a clear sign to discard it. Mold can grow on mayo stored in the fridge if the jar is not sealed properly or if a contaminated utensil was used.

Separation is normal in mayo and does not mean it has gone bad. If the oil rises to the top and the mixture looks thin, you can stir it back together. However, if the mayo smells sour, rancid, or off in any way, throw it out. A change in color—darkening or yellowing—can also signal spoilage, though some browning at the edges is normal over time.

The tricky part is that Salmonella contamination from leaving mayo out too long produces no visible or olfactory signs. This is why the two-hour rule is not optional—it is your only defense against a pathogen you cannot detect.

What to Do If Mayo Has Been Left Out Too Long

If you realize mayo has been sitting out for longer than two hours, or longer than one hour in heat above 90°F, discard it. Do not taste it to check if it is still good. Do not try to reheat it or cook it into something else. Heating mayo to high temperatures can break the emulsion and create a greasy, separated mess, and it will not kill Salmonella if it has already grown to high levels.

If you have eaten mayo that was left out too long and develop symptoms of food poisoning—nausea, vomiting, diarrhea, or fever—contact your doctor or call Poison Control (1-800-222-1222 in the U.S.). Most cases of Salmonella poisoning resolve on their own with rest and fluids, but severe cases may need medical care, especially for young children, older adults, or people with weakened immune systems.

The best approach is prevention: refrigerate mayo immediately after opening, use it within the recommended timeframe, and follow the two-hour rule whenever it is exposed to room temperature.

Frequently Asked Questions

Can I leave mayo out overnight if I put it back in the fridge?

No. Once mayo has been left out past two hours, bacteria have already multiplied to potentially unsafe levels. Refrigerating it after that point will not kill the bacteria or make it safe to eat. Throw it away and start fresh.

Is homemade mayo safer to leave out than store-bought?

No. Homemade mayo contains raw egg yolk just like store-bought, and it follows the same two-hour rule. Store-bought mayo is slightly more acidic, which slows bacterial growth a little, but both types can harbor Salmonella if left out too long.

What if mayo is in a sandwich—does the bread change the two-hour rule?

No. The sandwich as a whole follows the two-hour rule. Bread does not protect the mayo from bacterial growth. A mayo-based sandwich left out for two hours should be discarded, even if the bread looks and smells fine.

Can I freeze mayonnaise to make it last longer?

Freezing mayo is not recommended. Mayo is an emulsion, and freezing breaks down the structure, causing it to separate when thawed. The texture becomes grainy and unpleasant. Refrigeration is the best storage method for opened mayo.

Does adding extra lemon juice or vinegar to mayo make it safe to leave out longer?

No. While acidity slows bacterial growth, it does not stop Salmonella that is already present in the raw egg. The two-hour rule still applies, regardless of how much acid you add.