He's also losing tufts of fur from the back of his legs and his bum area. He's really fluffy in that area, so he's not getting any bald spots....
I did a little research on the internet and it looks like it's probably from an allergic reaction. It's not his food, so maybe he ate a bad bug... or got bit by one.
This happened to my mom's cat Mr. Tibbs a couple of years ago and the swelling dissapeared after a couple of days. (He didn't lose any fur though)
Has this happened to anyone else?