The blister is an irritating feature of sports participation, most commonly arising on the feet or hands of the athlete, where the athletic activity creates friction between an item of equipment making repeated contact against or along the surface of the skin. Often a very small object relative to the size of the athlete, blisters at their most innocuous are a distraction to the athlete as a result of their persistence; at their worst, they are an avenue for infection to enter the body and cause more serious harm.

The most frequent type of blister found in athletic participation is the friction blister, caused when the epidermis, or outer layer, of the human skin becomes separated from the dermis, the layer of skin below. This blister will result in a bubble-shaped lump under the skin surface. The bubble is taut, filled with serum, a clear, thin fluid, formed by its leakage into the blister bubble from the immediately adjacent skin tissues.

Common causes of friction blisters include: poor-fitting shoes or socks; an orthotic or other device is used for the first time (creating a different wear against the skin of the foot); instances when an athlete is required to handle an object that tends to move or slide through the hands (such as the handlebars of a mountain bike, ropes and winches in sailing, or a tennis racquet); or participating sports in which an object is thrown repetitively, such as a pitch in baseball.

The best treatment for a typical friction blister is to leave the blister alone. As annoying as this injury may be, a blister, properly bandaged and protected with an adhesive such as moleskin or protective gloves, will heal best if it remains intact. There is a temptation to puncture the blister dome, to drain off the seum beneath. This act increases the risk of infection entering the skin and removes the protective quality of the fluid.

A small blister (less than 0.39 in [1 cm]) is known as a vesicle; larger blisters are referred to as bullae. If the blister is punctured, or within two to three days pus is noticed in the blister, or the blister appears red or is sensitive to the touch, there is a strong likelihood that the blister has become infected and the injury should be attended to by a physician.

The second most common form of athletic blister is the aptly described blood blister. This type of skin injury results from either a direct blow to the skin, or when the skin is pinched as a result of being caught between two harder objects. An example of the pinching action causing the formation of a blood blister includes the hand of a cyclist caught in the chain of bicycle while making a repair.

As with the friction blister, the puncture of the blood blister surface to drain away the underlying fluid and reduce the apparent pressure on the surface of the skin is not recommended. A significant risk of bacteria entering the puncture opening will result. The blister, which typically will manifest itself very quickly after a pinch or blow, should be treated with

Tennis players often develop friction blisters on their hands and fingers from holding their racquets.
ice and it should be kept clean and protected by a bandage that is changed on a daily basis. A blood blister will typically take between seven and 14 days to resolve. If the blister is so large that there is interference in the normal function of the body part affected, the blister may be drained and treated; ideally, such a procedure should only be carried out in the sterile confines of a medical office. If conducted at home, the athlete should thoroughly clean and dry the affected area. Then a needle should be heated and used to penetrate the side of the blister to drain its content. Once drained, an antibiotic ointment should be applied; the dressing of the blister should be changed and the antibiotic reapplied daily.

Foot blisters are reduced, if not prevented, through careful attention to the fit of the shoes and socks to be used for the particular activity. Socks that direct perspiration away from the skin surface, a process known as "wicking," are also effective in blister reduction, as is the wearing of two layers of socks, one thick and one thin. In demanding, highly repetitive sports such as distance running, a layer of petroleum jelly applied between the runner's toes will reduce the degree of friction on the skin.

Other forms of blisters may arise in athletic activity, although less frequently than by friction or by pinching of the skin. Such problems occur chiefly through allergic reaction, through exposure to a chemical, or through contact with a poison such as poison ivy or poison sumac. Contact with such substances will cause the skin to blister and may be very contagious. Exposure to excessive sunlight, extreme cold, or extreme heat may also result in blistering to the skin.

SEE ALSO Abrasions, cuts, lacerations; First aid kits for sports; Skin and muscle blood flow during exercise.