It's probably from sitting outside. Same reason plastic headlights on cars get foggy after a while of being near the ocean. Once you clean it, and keep it inside now, it should be fine. My bike sat outside with no cover when I lived right on the beach on windward side of Oahu, literally could throw a rock in the water. After about a month or two I moved into a house with a garage and I used Back To Black on all my black parts and they look brand new. Some of the plastic trim pieces were faded pretty bad too. That stuff is awesome.