Refrigerate or Leave Out? The Truth About Mayonnaise Storage

That jar of mayonnaise sitting on the kitchen counter may look completely harmless. But when it comes to food safety, appearances can be misleading.

A sandwich sits out during lunch. The mayonnaise gets left on the counter while dinner is being prepared. Someone uses a knife for one ingredient, then dips it straight back into the jar.

Nothing looks wrong.

There may be no strange smell. No obvious change in color. No dramatic warning that tells you it is time to throw it away.

That’s exactly why proper storage matters.

So, does mayonnaise really need to be refrigerated?

For commercial mayonnaise, the answer is yes once the jar has been opened.

Commercial mayonnaise is typically made with pasteurized eggs and acidic ingredients, which help make it more resistant to harmful bacteria than homemade mayonnaise made with raw eggs. But that doesn’t mean it is designed to sit on a warm countertop for hours.

Once opened, follow the storage directions on the label and keep the jar refrigerated. FDA guidance also recommends that perishable foods not remain at room temperature for more than 2 hours—or just 1 hour when temperatures are above 90°F (32°C).

And there’s another habit worth changing:

Don’t put a used, food-covered knife back into the jar.

Instead, scoop out what you need with a clean utensil. It is a small step, but good food-handling habits help reduce the chance of contamination.

What about homemade mayonnaise?

This is where you should be more careful.

Traditional homemade mayonnaise can contain raw eggs that haven’t been cooked. USDA does not recommend eating raw shell eggs because of the potential for Salmonella. If you’re making homemade mayonnaise, using pasteurized eggs or pasteurized egg products is a safer choice. USDA recommends keeping homemade mayonnaise refrigerated and using it within four days when made with pasteurized eggs or egg products.

The simple mayonnaise rules worth remembering

🧊 Refrigerate opened commercial mayonnaise.

⏰ Don’t leave perishable foods sitting out for hours.

🥄 Use a clean utensil instead of dipping a used knife back into the jar.

🔒 Keep the lid tightly closed.

🥚 Be especially careful with homemade mayonnaise made from raw eggs.

📅 Check the manufacturer’s storage instructions and use-by guidance.

And perhaps the biggest mistake is assuming that “it smells fine” means “it’s definitely safe.”

Foodborne bacteria don’t always announce themselves with an unpleasant odor or obvious appearance.

You don’t need to be paranoid about mayonnaise.

You just need to store it properly.

Because when a tiny habit—like putting the jar back in the refrigerator—takes only a few seconds, there’s really no reason to gamble with food safety.