Do the white patches ever turn blue/purple or red afterward? If so, this could be Raynaud's phenomenon. I have it in just my feet. You should see a rheumatologist to get a proper diagnosis. It's really a benign vascular thing. But it can be significant in the big scheme of things. If there are no color changes, it may still be Raynaud's, but I would let a rheumatologist tell you about it.
Let me know if you have questions. It's something you can easily look up info on, I'm sure.
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