What causes certain plastics to get gummier over time?

[beowulff]

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Plastic and rubber coatings degrading and turning into a sticky mess

Not sure where to put this, but I guess it’s mostly mundane… More and more I’m noticing that plastic and rubber coverings on many of my electronics and other items – TV remote, ipod cover, wireless mouse, various grips and handles – have turned sticky and, well, just gross. I’ve used isopropyl alcohol to try to remove the coating with limited success, sometimes it works, sometimes it turns the coating even gooier and messier. Just wondering if others have noticed this and what kind of solution…