My dog sometimes has a few white spots on his nose, like crusts. What's that?
My cat has that when she's dehydrated, could that be the reason your dog gets it?
Some causes could be sunburn, wind burn or the heat in your home is causing it (dehydration).
Those are optimistic causes though. Please go see your vet, as it could be ringworm or other diseases.

Thanks for replying and sorry for not being on. I've been to the vet and it was just dehydration from the central heating at home. Glad that's all after reading what other things it could be!