Commercial mayonnaise is generally safe to eat shortly after its printed date, but how long depends on whether the jar has been opened and how it’s been stored. That date on the label is almost always a “best by” or “sell by” date, which indicates peak quality rather than a hard safety cutoff. Still, mayonnaise does eventually spoil, and knowing what to look for can save you from a miserable bout of food poisoning.
What the Date on Your Mayo Actually Means
“Best by” and “sell by” dates are manufacturer suggestions for when the product tastes its best. They don’t mean the food is dangerous the next day. Hellmann’s, one of the largest mayonnaise producers, states plainly that most food can safely be eaten after those dates as long as it’s been handled properly. The texture or flavor may start to decline, but the mayo doesn’t suddenly become toxic at midnight on the printed date.
There is one exception. If your jar carries an actual “expiration” date (sometimes printed as “EXP”), that’s a firmer deadline and you should discard it once that date passes. Most commercial mayo uses “best by” labeling, so check yours carefully.
Why Store-Bought Mayo Resists Bacteria
Commercial mayonnaise is more resilient than most people assume. The vinegar (acetic acid) in the recipe drops the pH to around 4.4 or lower, which is acidic enough to kill common foodborne pathogens like Salmonella and E. coli. A review published in the Journal of Food Protection found that pH adjusted with acetic acid is the single most important factor in destroying harmful bacteria in mayonnaise and dressings. At the acidity levels in commercial mayo, pathogenic bacteria simply can’t survive long enough to multiply to dangerous levels.
This is why mayo-based dishes like potato salad or chicken salad cause food poisoning far less often than people think. When those dishes do make someone sick, the culprit is usually the other ingredients (chicken, potatoes, eggs added separately) rather than the mayo itself.
How Long Mayo Lasts After Its Date
Unopened commercial mayonnaise stored at room temperature keeps for about three to four months past its production. Once you’re significantly beyond the best-by date on an unopened jar, quality drops and safety becomes less predictable. Past four months beyond the printed date, the risk of spoilage rises enough that discarding it is the smarter choice.
Once opened, the rules change. The USDA recommends using opened mayonnaise within two months of opening, kept refrigerated the entire time. Every time you dip a knife or spoon into the jar, you introduce new bacteria, and even the acidic environment can only do so much over time. If your opened jar has been sitting in the fridge for longer than two months, it’s time to let it go.
Temperature Matters More Than the Date
How your mayo has been stored matters at least as much as when it was made. Bacteria multiply rapidly in the “danger zone” between 40°F and 140°F. Perishable foods containing mayonnaise should not sit out for more than two hours at room temperature. If it’s a hot day above 90°F, that window shrinks to just one hour.
This is the real risk at summer cookouts and picnics. A jar of mayo that’s been left on a warm counter all afternoon is far more dangerous than a properly refrigerated jar that’s a week past its best-by date. If you can’t remember how long the mayo has been out, don’t risk it.
How to Tell if Mayo Has Gone Bad
Your senses are surprisingly good at detecting spoiled mayonnaise. Look for these signs:
- Color change: Fresh mayo is white to pale cream. Yellowing or darkening suggests breakdown.
- Separation: A thin layer of liquid on top is normal in older mayo and can be stirred back in. Large pools of separated liquid or an oily, watery texture throughout means it’s past its prime.
- Off smell: Fresh mayo smells mildly tangy. A sour, acidic, or rancid odor is a clear sign of spoilage.
- Unusual texture: Lumps, excessive thickness, or a slimy consistency are all red flags.
If anything looks, smells, or tastes off, throw it out. Food poisoning from spoiled condiments can cause diarrhea, vomiting, stomach pain, fever, and headaches, sometimes lasting several days.
Homemade Mayo Is a Different Story
Everything above applies to store-bought mayonnaise made with pasteurized eggs, vinegar, and preservatives. Homemade mayonnaise plays by very different rules. It contains raw egg yolks that haven’t been pasteurized, which means Salmonella is a real concern from the moment it’s made. Homemade mayo also lacks the commercial preservatives that extend shelf life.
Keep homemade mayo refrigerated at all times and use it within a week. There is no grace period past that point. If you’re making mayo at home and want a bit more safety margin, use pasteurized eggs, which are sold in most grocery stores alongside regular eggs.