
My dogs used to get these regularly. Then we moved house - 16 yrs ago - & I've never had any since (Not suggesting you should move - that's a bit drastic!), but it seems as though they were caused by something in the environment. I used to use purple crystals from the Chemists, can't remember what there called. Potassium Permanganate? Something like that? I'm sure someone else will know. I used to dissolve some in a jamjar of water & stick the dog's foot in the jar & they woud dry up quickly. I use Grass' for lots of things but the purple crystals seemed to work quicker. If you've got a light coloured dog it does make the fur brown for a while though.