This can happen when someone decides not store their mayonnaise after opening it for use on sandwiches or salad dressing  However , it doesn’t mean that they should toss their entire container because mayo stored properly doesn’t spoil like other foodstuffs  The reason behind its lack of refrigeration is because mayo does not contain any preservatives that can protect its original texture from spoiling as long as there is enough air around it This explains why mayonnaise can easily become rancid within hours after opening  For those who are concerned about their health might want take note that rancid oils could potentially contribute towards obesity when used excessively as fat absorption could be caused due to this oil  Thus we suggest using rancid oils moderately unless we are talking about butter (fat used on top) which we suggest using sparingly  Lastly; make sure you follow our mayo recipe properly so that this issue could never happen again!