We use CDs for digital archiving (music we've played, pictures we've taken, things we've written, etc.) and it's dismaying to think these things could soon perish.
Commercial CD burners burn pits into an aluminum substrate with a high energy laser. Home CD-Rs use a much lower powered laser to "burn" photo-reactive dye. Photo-reactive dye is photo-reactive. Sunlight contains a full spectrum (pretty much all) wavelengths of light. Leave a CD-R out in sunlight and it is likely to go bad.
Commercial CDs don't have this problem but the apparatus to make them isn't cheap.
Looking deeper? See:
How To Choose CD/DVD Archival Media (October 30, 2006) -- the conclusion: use only Taiyo Yuden CD+R and DVD+R media. Avoid CD-R, CD-RW, DVD-R, DVD-RW, and DVD+RW. Taiyo Yuden manufactures the highest-quality CD media.
Here is the Tayo Yuden FAQ.
Care and Handling of CDs and DVDs -- A Guide for Librarians and Archivists (50 pages)
Page 12: "How Long Can You Store CDs and DVDs and Use Them Again?"
Among the manufacturers that have done testing, there is consensus that, under recommended storage conditions, CD-R, DVD-R, and DVD+R discs should have a life expectancy of 100 to 200 years or more; CD-RW, DVD-RW, DVD+RW and DVD-RAM discs should have a life expectancy of 25 years or more. Little information is available for CD-ROM and DVD-ROM discs (including audio and video). Expectations vary from 20 to 100 years for these discs.
Here are suggested handling procedures.
Elsewhere, NIST recommends CDR media with a "gold metal" layer for archival purposes.
Quite a bit of research has been done on care and retention of CDs. The most important factors are:
Imation makes CD-Rs that have a lifetime guarantee.
If you burn a CD at 1x, each hole has more definition than if you burn it at 12x. This is because even a tiny electronic laser takes some time to turn on and off. The size of the dot and the spin rate combine to make this time cover a sizeable percentage of the hole. The longer you want to keep a CD, the longer you should take to burn it. Cheaply-burned CDs are said to last 12 to 24 months.
The closest surface to the data layer on a CD is the top. The gum in a paper label is going to speed up the break-down of the protective lacquer there. Use a sharpie, and nothing more.
Keep the really important ones in a cool dry place, without weight on them.
Here are the details and a good quick reference.