In an ordinary blister, a patch of the outermost layer of the skin (epidermis) has separated from the under layer (dermis). Friction from a rubbing shoe, for example, or a burn from a chemical action may cause this separation. The separated skin, deprived of nourishment, dies, but remains intact for several days if not disturbed. Meanwhile, the bloodstream reabsorbs the fluid in the blister and, beneath the blister, the dermis regenerates a new outer layer of the skin. After the blister collapses, the dead skin sloughs off.
Infection is the principal complication of blisters and dictates our treatment of them. If the blister is very large or likely to be bumped or broken because of its location, puncture it with sterile needle at its base to drain off the fluid. A small blister, left alone, will ordinarily heal in a few days. Treatment should be confined to keeping the site clean as a protection against bacterial invasion.
Since the blister is the best, protection for the wound, you should try to preserve it, whether intact or broken, until the skin beneath it is regenerated. Clean the area by soaking it in soapy water. A sterile Vaseline gauze over the blister will help to keep out dirt and protect the detached skin. The Vaseline prevents sticking and makes removal of the gauze easier after three or four days when the blister has collapsed. Soak the area in soap and water and rub gently to remove the dead skin.
If at any time pus appears in the blistered area, or if redness and swelling spreads out into the unblistered surrounding skin, you should get in touch with the doctor at once. Infection has probably set in.