If you have bacteria, such as staph, on your hands, you transfer it to salad ingredients when you cut them up. Since potatoes and hard-boiled eggs may be warm, bacteria can grow on them.
Commercial mayonnaise gives you a little protection, because it has acidity that keeps bacteria from growing so quickly. But that’s not enough to stop trouble when you leave potato salad out in the sun.
Make sure you wash your hands and don’t let potato salad sit out for more than an hour above 90 degrees.
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