Trouble with your footwear, or just too many miles in one day, can leave your feet blistered and raw. Since your skin has effectively been peeled away, these injuries should be treated like the open wounds that they are, and covered with an antibacterial material. Good candidates are plantain (Plantago major) and yarrow (Achillea millifolium). Crush either (or a blend of the two) into a paste and apply to the blister. Use some kind of bandage to keep the poultice in place, and take it easy until the skin heals, if possible.