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Claim Check

How Risky Is Mayo?

by Densie Webb Ph.d., R.d.  

The claim: Mayonnaise is a major source of foodborne illness.

The facts: This myth continues to circulate, even on some reputable websites. Granted, summertime picnic spreads that include heaping bowls of potato salad, chicken salad, tuna salad, and egg salad can easily be the source of food poisoning if these foods are left out in the heat. But here’s the thing: Commercial mayonnaise—made primarily of water, vegetable oil, and eggs—isn’t the culprit.

The mayonnaise myth began back when it was more common to make mayonnaise from scratch. But commercial mayonnaise doesn’t cause food poisoning for a couple of reasons. One is that it is made with pasteurized eggs, which carry virtually no risk of contamination. Second, commercially prepared mayonnaise must adhere to what’s known as a “standard of identity” set by the FDA—that is, it must be made with specific ingredients in a specific way. Two of the required ingredients for mayonnaise are vinegar and lemon juice, in set amounts. Both are acidic, and acid is the enemy of foodborne bacteria.

According to a review of literature, published in the Journal of Food Protection, Salmonella, E. coli, Listeria, and other harmful bacteria die when “inoculated” into mayonnaise. “Acidity is the most important intrinsic characteristic of mayonnaise, dressings, and sauces in determining the growth and the survival of pathogenic bacteria,” the paper noted. At the time of publication (2000), there had been no incidences of foodborne illness associated with commercially produced mayonnaise, giving it a “remarkable safety record.” There are no reports from the CDC since then, either.

The fact is, it is the ingredients that are commonly paired with mayonnaise that are the risky ones. Chicken, tuna, potatoes, and eggs, for example, are all less acidic than mayonnaise and thus more susceptible to bacterial growth. Combine that with temperatures above 40°F and any bacteria that may be present will double in as little as 20 minutes. If mayonnaise is part of the dish, bacterial growth is actually diminished, though mixing mayonnaise with contaminated ingredients doesn’t make a dish safe. Food safety rules still apply:

  • Wash hands and surfaces often during preparation.
  • Don’t cross contaminate (don’t mix raw foods with cooked foods).
  • Refrigerate perishable foods as soon as possible (40°F or below).
  • If mayo dishes, such as chicken salad or tuna salad, are on your picnic menu, bring them in a cooler packed with ice to keep them below 40°F. And keep in mind that the USDA recommends throwing out any perishable foods, such as meat, poultry, fish, eggs, and prepared foods, that have been at room temperature for more than two hours, and after one hour if the temperature is 90°F or above.
  • Refrigerating mayonnaise keeps it fresh longer. And the USDA advises discarding opened mayonnaise (as well as tartar sauce and horseradish) if it sits above 50°F for more than 8 hours. One concern is that the mayo could have been contaminated by other foods you have mixed with it (by using the same knife or spoon, for example), and those foods might encourage bacterial growth.