Should mayonnaise be refrigerated or can it be left out? Learn how long mayonnaise can safely stay at room temperature, why refrigeration matters, and the signs that it should be thrown away.

Refrigerate or Leave Out? The Truth About Mayonnaise Storage

Mayonnaise is one of those everyday foods that can cause confusion in the kitchen. Some people keep it in the refrigerator immediately after opening, while others leave the jar on the counter for hours—or even days.

So, what is actually safe?

The answer depends on whether the mayonnaise is opened, how long it has been sitting out, and the temperature around it.

Does Mayonnaise Need to Be Refrigerated?

Yes. Commercial mayonnaise should generally be refrigerated after opening.

Store-bought mayonnaise is made with ingredients such as eggs, oil, and an acidic ingredient like vinegar or lemon juice. The acidity and commercial processing help make unopened mayonnaise relatively shelf-stable.

However, once the container is opened, refrigeration is the safest way to maintain its quality and reduce the risk of spoilage.

An unopened commercial jar can usually be stored in a cool, dry pantry until its best-by date, provided the manufacturer’s instructions don’t say otherwise.

How Long Can Mayonnaise Sit Out?

This is where you need to be careful.

As a general food-safety rule, perishable foods shouldn’t remain at room temperature for more than 2 hours. If the temperature is above 90°F (32°C), that window drops to about 1 hour.

That means leaving an opened jar of mayonnaise on the kitchen counter throughout the day isn’t a good idea.

Even if the mayonnaise looks perfectly normal, harmful bacteria aren’t always visible or detectable by smell.

What If You Accidentally Left It Out Overnight?

If an opened jar of mayonnaise was left at room temperature overnight, the safest choice is to discard it rather than put it back in the refrigerator and continue using it.

Refrigeration slows bacterial growth; it doesn’t reverse what may have happened while the food was sitting in unsafe temperatures.

This becomes even more important with mayonnaise-based foods such as:

• Chicken salad
• Egg salad
• Tuna salad
• Potato salad
• Sandwiches containing mayonnaise
• Creamy dips and sauces

These mixtures can become more perishable because additional ingredients are involved.

Why Does Refrigeration Matter?

Cold temperatures slow the growth of microorganisms that can spoil food or potentially cause illness.

Refrigerating mayonnaise also helps preserve its texture, flavor and appearance. Warm temperatures can cause the oil and other ingredients to separate, making the mayonnaise thinner or less pleasant to eat.

Keeping the jar consistently refrigerated is therefore a simple habit that protects both food safety and quality.

What About Homemade Mayonnaise?

Homemade mayonnaise deserves extra caution.

Unlike many commercial products, homemade mayonnaise may contain raw or lightly cooked eggs and doesn’t necessarily have the same processing and acidity controls as commercially produced mayonnaise.

If you’re making mayonnaise at home, use pasteurized eggs or pasteurized egg products when possible, keep it refrigerated, and follow a short storage period rather than treating it like a commercially manufactured jar.

Does the Smell Tell You If Mayonnaise Is Safe?

Not always.

A bad smell, mold, unusual discoloration, bubbling, or significant separation can certainly indicate that mayonnaise should be thrown away.

But the absence of these signs doesn’t guarantee that the food is safe.

That’s why time and temperature are more reliable considerations than simply smelling or tasting the mayonnaise.

The Best Way to Store Mayonnaise

For an opened jar, follow these simple habits:

1. Refrigerate it promptly after opening.
2. Keep the refrigerator at 40°F (4°C) or below.
3. Don’t leave the jar sitting on the table during a long meal.
4. Use clean utensils rather than dipping dirty knives or spoons into the jar.
5. Keep the lid tightly closed.
6. Check the manufacturer’s storage instructions and use-by/best-by information.
7. When in doubt about mayonnaise that has been left out for too long, throw it away rather than taking a risk.

The Bottom Line

The idea that mayonnaise is safe to leave on the counter simply because it contains vinegar or other acidic ingredients is misleading.

Unopened commercial mayonnaise can generally be kept in the pantry according to the manufacturer’s instructions, but opened mayonnaise should be refrigerated. If it has been sitting at room temperature for several hours—especially overnight—the safest decision is to discard it.

A few seconds spent putting the jar back in the refrigerator can save you from an unnecessary food-safety risk.