Why do aeropress columns get abrasions, or scars, near the top? A friend and I both have aeropresses that have been through 2-4 years of use. I noticed that mine has what looks like coffee-stained abrasions near the top of the column, furthest away from the filter. This is usually the region where the water surface is at longest, before I end up pressing it. No amount of washing seemed to get rid of the abrasions so they must be baked in to the plastic now. My friend confirmed he had a similar experience with his. Due to the rugged surface, it probably increases the chance of upward-leaks while pressing down on the plunger.

Is this due to some reaction occurring (unlikely I would think), or is it due to heat rising to the top (also seems somewhat unlikely to me)?

Update: Photos
However I cannot understood the scars definitely, I would like to offer a solution to the scars I thought:

There is a possibility that coffee grounds may stick to the rubber ring and scratch the plastic column when pressure is applied as they stay in between the rubber ring and the plastic column. Still, these scratches do not affect the performance of the gadget if they are not large enough to leak.

Easiest way to clean the grounds is rubbing the surface of the rubber ring by your finger under warm water for a few seconds.

Edit: After I see the photos, my guess is, these scars are caused by the scratches first, then the polished surface of the plastic is peeled off by heat. I assume you may continue to use it without problems. For other people with brand new aeropress, my previous advice still holds: try to wash away residual grounds off the rubber ring.