How do I stop a the tip of my shoes from curling up? ?

I live in the USA and thus officially wear the US size of 6. I bought a few years ago a pair of Adidas Samba Clics and found that after a short time the tips started to curl upward. This same thing happened to my Puma Lowcat's a year ago after wearing them for awhile. I measured my foot as a 6 (these two shoes were 7's). I can't find Puma Lowcat's any smaller then 7, and the Adidas Samba's I've Only found in the size 6 and a half. Is there a way to stop this "Shoe Curl"? What's causing it? Is it the Extra inch of shoe my toes don't cover when walking?