My sister is getting wide spread blisters on the top of her hands and feet (not the palms or bottom of feet). The blisters pop on their own and leave behind extremely slow healing sores. There are no rings around the blisters or sores, no recent medication changes, no allergies she has come in contact with, and no new stressors in hher life. She has been tested for anything infectious (like Mersa), and other tests to make sure there are no allergies, medication problems, or anything like scabies or shingles. What could it possibly be?