Blisters are the accumulation of fluid between the inner and outer layers of the skin. They are rarely a serious concern, but can become infected and more problematic if not treated correctly.
Blisters are caused by prolonged friction between your foot, socks and shoes.
A blister should be opened as soon as possible. The skin layers will then stick together and allow for a speedy return to activity. If conditions permit, first swap the blister with an antiseptic solution and then prick it with a clean needle that has been heated in a flame. Drain the blister, but leave the skin. Cover the area with a bandage and antibiotic cream or ointment. You should be able to expose the dried-up blister to air again in approx. 48 hours. If blisters are excessively painful, persistent or infected see your doctor or podiatrist for treatment.
Dual-layer or blister-free socks will minimize friction and moisture and help keep you less susceptible to blister formation. (Breathable synthetics are excellent for keeping your feet dry). Neoprene insoles may also help reduce friction. Break in new shoes gradually, and make sure that your shoes fit your feet properly, in both length and width and are also correct from a biomechanical point of view. This is important as too much foot motion can cause friction leading to blister formation.
None, but let comfort be your guide.