Unfortunately, there are some discs being manufactured which may not stand up to the test of time. Actually, all data storage media, from floppy disks to computer tapes, degrade slightly over time. The key factors are how much degradation happens, how fast, and what was the error rate when the media was new. The most common way for CDs to degrade is that the metal layer inside the disc starts to corrode. This corrosion causes small "pock marks" to form on the metal layer. These corrosion spots look just like data "pits" to the readback laser, so errors are introduced. These additional errors also take away from the extra error correction that would normally be used to correct for more normal defects such as scratches and fingerprints. Of course, the error correction chips in the player can still correct for some of these errors, but when the number of errors become too large, the data may be unreadable even with error correction. Quality CD-ROM discs will have low initial error rates, and will degrade very slowly, if at all. This insures the highest probability that the data will stay accessible for a long time.

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