Leif Parsons
This is the time of year when food poisoning typically spikes, and one popular picnic ingredient that always attracts suspicion is mayonnaise.
But studies cast doubt on that.
Most commercial brands of mayonnaise contain vinegar and other ingredients that make them acidic — and therefore very likely to protect against spoilage. When problems occur, they usually result from other contaminated or low-acid ingredients (like chicken and seafood), improper storage and handling, or homemade versions that contain unpasteurized eggs.
One prominent study published in The Journal of Food Protection found, for example, that in the presence of commercial mayonnaise, the growth of salmonella and staphylococcus bacteria in contaminated chicken and ham salad either slowed or stopped altogether. As the amount of mayonnaise increased, the rate of growth decreased. When temperatures rose to those of a hot summer day, the growth increased, but not as much as in samples that did not contain mayonnaise.
For backyard chefs, some high-risk foods in summer are raw shellfish, bulk ground beef (health officials say a single hamburger can contain meat from hundreds of animals) and unwashed fruits and vegetables.

Despite its reputation, mayonnaise can reduce food spoilage.