Wow, very perplexing. And it's not sunburn, correct? I can't imagine what would cause the blistering and pain on the tops of your feet. Please let us know what you find out.
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major sunburn was my immediate thought. I don't know anyone who rubs lotion onto their toes, and foot sunburn is the worst for people who don't go bare foot often. Sunburn can cause blistering, swelling and pain. I usually try to bury my feet in the sand when sitting on the beach, to keep the sun off of them.