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First time home owner here. I stuck these vent deflectors a month ago on one of our vents and I removed it today for some other reason. I noticed these stains that looked like water stains but I think it's actually something that is growing - maybe unfortunately mold or something. I need help in understanding this situation and possibilities of this happening. Please share your experience or knowledge related to this issue if you can.
Thank you!
EDIT: Mystery solved - this seems to be the result of some chemical spray during cleaning. Not concerning.
The shape of the stain and the spread of the dots look a lot like a spray to me. The large stain is where the centre of the spray hit, the smaller dots are where it misted out / splashed from the centre, and the neat clear line across the middle looks like the front of the acrylic piece protected part of the back / inside because of the angle of the spray. If it's mounted the same way up as you're holding it in the photo, it would make sense based on someone spraying upwards towards the top of the window.
As remotelove said, some chemicals can damage plastics, and that's what I think has happened here.
Sounds right to me. Mystery solved.