Is there any risk of illness from eating store-bought mayonnaise?

Very little. Commercial mayonnaise is a very safe product for three reasons:  because it is heat processed in the jar, commercial mayonnaise is sterile until it is opened because it’s been heated to a temperature sufficient to render pathogenic bacteria inactive; the lemon juice or vinegar makes it very acidic; it contains salt and chemical preservatives. This combination creates an environment that stops the growth of dangerous bacteria. Moreover,  studies show that hazardous bacteria actually die off when put into commercially-prepared mayonnaise.  Occasionally, commercial mayonnaise has been accused of causing illness, but then investigation has shown that  the bacteria came from some low-acid food it was mixed with, such as chicken or potatoes.  Commercial mayonnaise is actually  somewhat protective because of  its tendency to stop the growth of and even  kill off  harmful bacteria that may be in foods it’s combined with.
 
 
Source(s):
The Association for Dressings and Sauces  “Food Safety: Make Mine Mayonnaise and “Mayonnaise, the Misunderstood Dressing”
 
Susan Brewer, Ph.D., University of Illinois, Department of Food Safety and Human Nutrition