Cantharidin. Your doctor "paints" cantharidin on your wart and covers it with a bandage. This is generally painless. The cantharidin causes the skin under the wart to blister, lifting the wart off the skin. When the blister dries, the wart comes off with the blistered skin. You may feel some pain when the skin blisters. When you see your doctor again, he or she will remove the dead skin and may retreat.