A blister is a small bubble of liquid trapped beneath a layer of dead skin. Blisters tend to break open by themselves, releasing the watery fluid trapped within them. They are generally not regarded as a serious medical problem.
Blisters usually form at a localized area on the skin as the result of a burn, impact injury, exposure to chemical or sunlight, rubbing, or freezing. The liquid bubble consists of water and proteins released by injured tissue. Most blisters heal rather quickly on their own without leaving scars or other evidence of their presence. Blisters resulting from systemic disease may take longer to heal and may leave permanent scars.
Perhaps the most common cause of blisters is friction that occurs when skin rubs against socks, shoes, gloves, clothing, or other materials. The blister develops in the region of the outer layer of the skin (the epidermis) called the stratum lucidum. If you rub your finger across the top of a desk, that action causes some stress on the stratum lucidum. But normally that stress is not sufficient to produce any harmful effect. If you repeat that rubbing process for a longer period of time and use more pressure on the desk, stress on the stratum lucidum becomes greater, and it may actually tear loose from the epidermal layer beneath it. If tearing does occur, plasma from epidermal cells is released into the space beneath the outermost layer of epidermis, and a blister forms. Because the stratum lucidum contains no blood vessels, the cellular fluid is a clear, transparent liquid, and the blister does not bleed. The cellular fluid actually has a biological function in promoting healing and reattachment of the stratum lucidum. As healing occurs, the cellular fluid is reabsorbed by the epidermis, and the blister gradually disappears.
A number of other factors also cause blistering, including extreme temperatures, exposure to chemicals, crushing or pinching, and certain diseases. Some of these factors are closely related to friction blisters. For example, pinching one's skin in a door may produce a blister caused by tearing of the stratum lucidum, but the blister may also contain blood because damage to other parts of the skin has also occurred. Such blisters are sometimes known as “blood blisters.” Blisters that result from exposure to sunlight or intense heat are known as “heat blisters.” The precise mode of action for other types of blisters is not always known. Chemicals that can cause blistering (called vesicants) probably cause various types of damage to essential biochemical molecules (such as DNA and enzymes) within a cell, causing cell death that leads to the development of blisters. Itchy, blistered skin caused by exposure to a chemical is called “contact dermatitis.” A number of chemicals have been developed for use in warfare that has such effects. Among the many everyday products that can cause blistering are soaps, shampoos, perfumes, and cosmetics; certain types of plants, such as poison ivy and poison oak; certain types of metals; household cleaning products; and certain types of over-the-counter and prescription medications.
Certain diseases may also cause blisters, the most common of which are chickenpox, herpes, impetigo, and a type of eczema called dyshidrosis. Less common blister-causing diseases are bullous pemphigoid, pemphigus, dermatitis herpetiformis, chronic bullous dermatosis, cutaneous radiation syndrome, and epidermolysis bullosa. These conditions all have more severe and extensive symptoms than do simple forms of blistering and are regarded as more serious medical conditions.
Blisters are easily diagnosed simply by looking at them. They have a very distinctive physical appearance that nonprofessionals can easily recognize.
In the vast majority of cases, simple blisters heal on their own within a matter of days. Blisters caused by temperature extremes, chemicals, and sunlight may take longer to heal, and should be closely observed for secondary problems, such as skin infections. Blistering that results from diseases generally recur until the disease itself has been treated.
The risk of developing friction blisters can be reduced by reducing the friction between skin and clothing. For example, foot blisters can be prevented if one is careful to select shoes that fit well and to wear well-fitting, comfortable socks at all times. Hand blisters can be avoided by wearing gloves when one is participating in activities that might result in the formation of blisters, such as working with tools or playing golf. The use of talcum powder in both shoes and socks and in gloves can also reduce the amount of friction between the body and clothing. If one plans to go on a long hike or to work with tools for a long time, the risk of blisters can also be reduced by placing adhesive tape over the region of the skin where friction is most likely to occur. Blisters caused by exposure to sunlight can be reduced by wearing a sunscreen. Chemical blisters are less likely to occur if a person finds out the substances to which he or she is sensitive (such as certain soaps or household products) and then avoiding those substances.
See also Golf ; Walking
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American Academy of Dermatology, PO Box 4014, Schaumburg, IL, 60168, (847) 240-1280, (888) 462-3376, Fax: (847) 240-1859, http://www.aad.org .
David E Newton, AS, MA, EdD