posted on Feb, 7 2007 @ 08:55 PM
The only toxin I can think of is salmonella from the eggs if you make your own at home.
I don't see any reason you can't put some mayonnaise on a sandwich and toss it in the microwave to warm it up.
The danger comes from leaving a potato salad out for a number of hours in a salad bar that isn't properly chilled, or egg salad sandwiches left for a
long time without refrigeration.
And even in those two cases the bacteria that grows is something that was on the cooks hands or the surfaces it was prepared on.
That jar of Kraft or Hellman's you buy at the grocer won't pose any danger that I know of.
If you do make your own at home, keep it chilled, and use it within a few days.