Ouch! You pinched your finger and voila, you have a blister. But this is a blister with a difference and it is filled with blood. Wondering how to treat a blood blister? Best thing to do is elevate it, use a bag of peas or run it under cold water or soak it in Epsom salts to help keep the swelling down. Try not to pop the blister to help avoid infection but in the event the blister does pop treat .