Food poisoning..?!

Food poisoning..?

Hi,
They say, you should not leave left-over food outside in summer(Keep it in fridge). It may cause food poisoning. Could someone pl explain the technicalities involved. I mean, what happens if you leave it outside . Sth to do with fermentation,bacteria growth ec etc? Also any idea of the time frame?
Thanks

Refrigeration of left-over foods decreases the dangers of bacteria overgrowth in them. Heat and humidity are excellent enviroments for bacterial reproduction. The time frame is under an hour if the outside temp is over 90° and up to 2 hours if it's under that, but you should really store them in a container with lid as soon as you are done eating and store it in the fridge.