Blisters are small pockets of fluid within the upper layers of the skin, typically caused by forceful rubbing, burning, freezing, chemical exposure or infection.
Blisters on foot are caused by the improper footwear condition which is applied when the player's character wears any shoe on the wrong foot (e.g., wearing a left shoe on the right foot) and develop if he is suffering from it for more than one hour. Wearing the makeshift rag shoes. regardless on which foot, also causes the same result.
Having blisters reduces the number of available moves per turn by one and also cause some pain.
The blisters cannot be healed in any way, but will go away on their own, after three days (72 hours/turns) from showing up. There is no way to counter-act the movement penalty in any way, but the pain can be mitigated with the use of painkillers or alcohol.
Once applied the blisters will start healing, even if their initial source (the improperly worn footwear) is still in place, and once healed will not appear again. However, if the uncomfortable shoe is removed and then put back on, the whole process will re-start.