There is an old wives tale stating that you cannot heat mayonnaise. That may have been true when mayonnaise was still made with only raw eggs and oil, but commercial mayo now has preservatives and vinegar added to make it resistant to bacteria. In fact, mayonnaise used in ham salad, tuna salad and chicken salad will actually slow the growth of bacteria on those meats. It isn't advisable to leave mayo out in the hot sun for hours, but a little warming used for cooking or heating leftovers is perfectly safe.
Measure the amount of mayonnaise you wish to heat.
Place the mayonnaise in the microwave, or if using in a sauce like Hollandaise and Béarnais, place the mayonnaise in a pan or skillet on the stove.
Allow the mayonnaise to heat in the microwave to 10 to 30 seconds. Time will vary based on the size and wattage of your microwave. For sauces, determine the length and temperature to heat the mayo by following the directions of the recipe.
Select a prewarmed item to which you would like to add mayonnaise.
Measure the desired amount of mayonnaise.
Add the mayonnaise to the already warmed food for indirect heating. This could be foods like cooked hamburgers, BLTs or anything else you would like topped with mayo.