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A BLISTER is a small pocket of body fluid (lymph , serum , plasma , blood , or pus ) 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, either serum or plasma. 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 . In dermatology today, the words vesicle and bulla refer to blisters of smaller or greater size, respectively.

To heal properly, a blister should not be popped unless medically necessary. Once popped, the excess skin should not be removed because the skin underneath needs that top layer to heal properly.

CONTENTS

* 1 Causes

* 1.1 Friction or rubbing * 1.2 Extreme temperature * 1.3 Chemical exposure * 1.4 Crushing/pinching * 1.5 Medical conditions

* 2 Pathophysiology

* 2.1 Friction blisters

* 3 Prevention

* 3.1 Friction blisters * 3.2 Other

* 4 References * 5 External links

CAUSES

A 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.

FRICTION OR RUBBING

Picture of various size blisters on the sole of a foot due to friction.

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 walking long distances or by wearing old or poorly fitting shoes. Blisters are most common on the hands and feet, as these extremities are susceptible while walking, running, or performing repetitive motions, such as joystick manipulation whilst playing certain video games, digging with a shovel, playing guitar, etc. 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).

EXTREME TEMPERATURE

A blister caused by burning .

The time of blistering is one of the tools used to determine the degree of burns sustained. First and second degree burns may result in blistered skin; however, it is characteristic of second degree burns to blister immediately, whereas first degree burns can have blisters after a couple of days. Blisters can also form on the hands and feet as a result of tissue damage incurred by frostbite .

CHEMICAL EXPOSURE

Blisters caused by exposure to sulfur mustard agent.

Sometimes, the skin will blister when it comes into contact with a cosmetic, detergent, solvent, or other chemical such as nickel sulfate , Balsam of Peru
Balsam of Peru
, or urushiol (poison ivy , poison oak , poison sumac ). This is known as contact dermatitis . Blisters can also develop as a result of an allergic reaction to an insect bite or sting. Some chemical warfare agents, known as blister agents or vesicants, cause large, painful blisters wherever they contact skin; an example is mustard gas .

CRUSHING/PINCHING

A blood blister usually forms when a minute blood vessel close to the surface of the skin ruptures (breaks), and blood leaks into a tear between the layers of skin. This can happen if the skin is crushed, pinched or aggressively squeezed.

MEDICAL CONDITIONS

There are also a number of medical conditions that cause blisters. The most common are chickenpox , herpes , impetigo , and a form of eczema called dyshidrosis . Other, much rarer conditions that cause blisters include:

* Bullous pemphigoid : a skin disease that causes large, tightly filled blisters to develop, usually affecting people over the age of 60. * Pemphigus : a serious skin disease in which blisters develop if pressure is applied to the skin; the blisters burst easily, leaving raw areas that can become infected. * Dermatitis herpetiformis : a skin disease that causes intensely itchy blisters, usually on the elbows, knees, back and buttocks. The blisters usually develop in patches of the same shape and size on both sides of the body. * Chronic bullous dermatosis : a disease that causes clusters of blisters on the face, mouth or genitals. * Cutaneous radiation syndrome
Cutaneous radiation syndrome
* Epidermolysis bullosa

PATHOPHYSIOLOGY

FRICTION BLISTERS

Friction blisters are caused by excess shear stress between the surface of the skin and the body. The strata of skin around the Stratum spinosum
Stratum spinosum
are most susceptible to shear. As the Stratum spinosum tears away from the connecting tissues below, plasma from the cells diffuses out. This plasma solution helps new cells divide and grow into new connective tissues and epidermal layers.

The clear fluid will be reabsorbed as new cells develop and the swollen appearance will subside. Painful blisters located on hands (palmar surface) and feet (plantar surface) are due to tissue shearing deeper in the epidermis, near nerve endings. Lower tissues are more susceptible to infection.

PREVENTION

FRICTION BLISTERS

Friction blisters, caused by rubbing against the skin, can be prevented by reducing the friction to a level where blisters will not form. This can be accomplished in a variety of ways.

Blisters on the feet can be prevented by wearing comfortable, well-fitting shoes and clean socks. Inherently ill-fitting or stiffer shoes, such as high heels and dress shoes, present a larger risk of blistering. Blisters are more likely to develop on skin that is moist, so socks that manage moisture or frequent sock changes will aid those with particularly sweaty feet. While exercising or playing sports, special sports socks can help keep feet drier and reduce the chance of blisters. Before going for a long walk, it is also important to ensure that shoes or hiking boots have been properly broken in.

Even before a "hot" or irritated area on the foot is felt, taping a protective layer of padding or a frict