What could be causing these sore spots on my dogs pads?

It has happened twice now, but far apart from each other. My dog will not stop licking her foot and when I look at it there's a red spot on one of the toes usually, it has been two different places on the same toe. It doesn't look like a cut but I could be wrong. To me it looks like it's been rubbed sore. I usually put it in warm water for a while, put Neosporin on it, and let her rest and it goes away in a day or so. What could cause it? I can't think of what would be rubbing if that is it. I don't make her walk on hot concrete so I doubt that's it. Any ideas?