Every time a plastic surface is scratched or chafed, or rubs against a rough surface, near invisible plastic dust particles break off and disperse into the environment. You breathe them into your lungs, they settle onto your food and drink and enter your stomach.
Some of them get permanently wedged inside your body. Now imagine a big, unshapely sculpture the size of a chair appears inside your house and you can't get it out for some reason. Sure, your world doesn't end, but it takes up space. How many would have to accumulate until they really started hindering your daily routines? That's what your cells feel like.
Most bubble gum is plastic for fuck's sake. People chew on plastic on a daily basis. (Good news is plastic-free chewing gum have appeared on the market.)