• If you are unable to get Illustrator to boot and see that Illustrator is crashing as it shows “loading fonts”.
• If your font list becomes filled with font names that look like they are combinations of other font names.
• Other weirdness with the behavior of your fonts.

The font caches are temp files that both your computer and Illustrator cooks up to keep track of what fonts are active and where they are located. There is no danger in deleting them, they will be recreated the next time you restart Illustrator in the case of the application level caches or by the finder in the case of the system level caches. Office also creates its own, which behave the same way, but, well, for Office.

How?

You can do this a few ways, but the easiest is to use the free app FontNuke on the Mac or CCleaner on Windows.
The functionality is also built into FontExplorer which used to be free, but now costs about as much as its competitors.
You could also do it manually, but why, when there are all the free apps to do it for you safer and easier?

To do it manually:

If you insist…

On the Mac.

Shut down all Adobe apps and do a search for “AdobeFnt”  There ought to be a bunch of them, most with a 2 digit number (eg.: “AdobeFnt56″) after them.  Any of them that have the .lst extension can be safely deleted.  Do not delete AdobeFnt.db or FontNames.db!! Those are not caches.

That takes care of the Adobe caches – now onto the OSX caches – and there’s a few of them.

OSX 10.4 and later has the capability built in to clear them itself – Just restart holding the shift key to boot into “safe mode” which will also clear out all your caches. After that, restart as usual and you should be back in business.

If that fails or you really want to do it yourself, here’s the list of OSX’s font caches:

• com.apple.ATS.System.fcache
• com.apple.ATSServer.FODB_System
• /Library/Caches/com.apple.ATS
• /Library/Caches/com.apple.ATS/501/Classic.fcache
• /Library/Caches/com.apple.ATS/501/Local.fcache
• /Library/Caches/com.apple.ATS/501/System.fcache
• /Library/Caches/com.apple.ATS/501/FondResourceCache
• /Library/Preferences folder: com.apple.ATS.plist
• /System/Library/Caches/com.apple.ATS.System.fcache
• /System/Library/Caches/fontTablesAnnex

Any time you delete the system caches, you must restart your computer.

On Windows

The Adobe caches are located at C:\Program Files\Common Files\Adobe\TypeSpt and delete any AdobeFnt*.lst files. Do not delete AdobeFnt.db or FontNames.db!! Those are not caches. As with the Mac, make sure that no Adobe apps are running when you delete them.

The Windows caches are

Windows NT, 2000, XP and Vista C:\WINDOWS\system32\FNTCACHE.DAT

Windows 95, 98, and Me (you pour soul) C:\WINDOWS\ttfCache

Yeap, one file.  Restart if you delete it.

Don’t go yet!

If after trying all of these options it’s still failing, let me know below in the comments (I really do read them) or try the links to the right.  And if it does work for you, let me know and don’t forget to check out the rest of the site.

Quit Illustrator and as you are restarting it:

On the mac – hold option-command-shift or on the PC – hold alt-control-shift

Some versions will bring up a dialog asking if you want to delete your prefs, some versions just delete them.

If this fails to solve your problem you can manually remove the preference folder (yes, folder).  It will be recreated the next time you start Illustrator.

On the Mac, it’s located at HD\Users\your_username\Library\Preferences\Adobe Illustrator CS# Settings\(localization folder)\

On the PC, C:\Documents and Settings\your_username\Application Data\Adobe\Adobe Illustrator CS# Settings\ Or something close to that, based on your version of Windows.

You can throw away the entire folder there, or rename it if you prefer, and Illustrator will create a new one in place of the old one the next time it’s started up.  Renaming it gives you the option of trial and error’ing the old files back in place if there are certain preferences you’d like to keep.

If all this fails, you can bring out the big guns and try the Cleaner Tool, provided by Adobe.  This will require you to uninstall everything from the creative suite and will require a re-install, so make sure you have some spare time (and your install discs) before you go that route.  It will remove all the cache files and additional noise installed by the apps to be sure that none of them have gotten corrupt.

If after trying all of these options it’s still failing, let me know below in the comments (I really do read them)  or try the links to the right.  And if it does work for you, let me know and don’t forget to check out the rest of the site.