I actually disagree with this cooking MYTH.

But; it depends on the TYPE of plastic. Don't trust takeaway containers or soft and flexible plastics.

Hard and rigid plastics are in fact SAFE if marked as "Microwave-Safe"; they HAVE TO BE SAFE to have that marking.

DO:

• avoid soft plastics
• avoid takeout containers
• avoid heavily damaged tupperware
• replace old tupperware plastics once in a while; especially if they're all scratched/dinged up.