If you have a blister which is painful when you walk it will cause excruciating pain... until it is popped. The important thing is that the blister does not become infected and so if you can have this opened and drained professionally, under sterile conditions, then it is advisable to do this. If you must pop it yourself then always drain it at the bottom (to allow the fluid to run down and out) and use a pin or needle which has been cleaned with boiling water beforehand. Clean with warm salt water and apply a clean sterile dressing over the open blister. Keep the blister dry and use a dry antiseptic spray over the site. If the blister is irritated by general footwear use a Compeed blister plaster, as it will make it more comfortable and encourage healing.