Blisters is a small pocket of fluid within the upper layers of the skin, typically caused by forceful rubbing (friction), burning, freezing, chemical exposure or infection. Most blisters are filled with a clear fluid called serum or plasma (aka, "blister water"). However, blisters can be filled with blood (known as blood blisters) or with pus (if they become infected).

The word " blister " entered English in the 14th century. It came from the Middle Dutch "bluyster", and was a modification of the Old French "blostre" which meant a leprous nodule -- a rise in the skin due to leprosy.

Blister may form when the skin has been damaged by friction or rubbing, heat, cold or chemical exposure. Fluid collects between the epidermis--the upper layer of the skin--and the layers below. This fluid cushions the tissue underneath, protecting it from further damage and allowing it to heal.

Intense rubbing can cause a blister , as can any friction on the skin if continued long enough. This kind of blister is most common after wearing a new pair of shoes. Blisters are most common on the hands and feet, as these extremities are susceptible while walking, running, or performing repetitive motions. Blisters form more easily on moist skin than on dry or soaked skin, and are more common in warm conditions. Less aggressive rubbing over long periods of time may cause calluses to form rather than a blister. Both blisters and calluses can lead to more serious complications, such as foot ulceration and infection, particularly when sensation or circulation is impaired, as in the case of diabetes, neuropathy or peripheral artery disease (PAD).

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