Foot blisters are among the most common injuries for athletes. According to research from the Scholl, over 5.2 million people suffer blisters every year. In a study of lower extremity injuries that occurred at the New York City Marathon, the most common foot problems reported were acute shear and stress injuries resulting in blister formation. Aside from being painful, blisters can alter an athlete’s running form and lead to even more serious injuries of the leg and hip due to irregular gait biomechanics. Blisters result from frictional forces that mechanically separate epidermal cells at the level of the stratum spinosum. Hydrostatic pressure causes the area of the separation to fill with lymph-like fluid. The magnitude of the frictional forces and the number of times an object cycles across the skin determine the probability of blister development. The higher the frictional forces, the fewer cycles are necessary to produce a blister. Moist skin increases frictional forces, leading to blister formation, while very dry or very wet skin decreases frictional forces, preventing blisters. Other risk factors for foot blister formation include ethnicity (African-Americans are at lower risk than others), flat feet and feet with structural prominences, such as bunions, hammertoes and Haglund’s deformity. Tips About Shoes, Insoles And Socks You Can Pass On To Patients In order to prevent blisters, we need to minimize friction. This begins with shoe selection. Emphasize to patients that their shoes should fit comfortably, with about a thumb’s width (3/8-inch to 1/2-inch) between the longest toe and the end of the shoe. Narrow shoes can cause blisters on the hallux and fifth toe. A shallow toe box can lead to blisters on the tops of the toes, while loose shoes often create blisters on the tips of the toes. Shoes should be sport specific. When trying on shoes, athletes should wear the same sock, insoles or orthotic inserts they wear when playing or working out. Encourage them to get shoes fitted in the afternoon or evening, since feet tend to swell during the day. Athletes should wear their shoes around the house for one to two hours to identify any areas of discomfort. It often helps to break in shoes by wearing them for one to two hours on the first day of sports activity and gradually increase use each day. However, even if shoes fit well, the insoles (or sock liners) could cause problems if they have worn out or flattened down. Remind athletes to check the condition of the insoles periodically and replace them if necessary. A new OTC insole (such as those manufactured by Spenco Medical Corporation) can keep friction to a minimum. Also encourage runners to examine the inside of footwear for seams or rough areas that often correspond to the sites of blisters. Emphasizing the proper socks also can decrease friction and prevent blister formation. Socks made from synthetic blends are best. Socks made from polypropylene or other new synthetic materials can wick moisture away from the skin more effectively than wool or cotton, further decreasing the likelihood of blisters. Layering socks or special double-layered socks can further minimize shearing forces. If your athletes wear socks with large toe seams, tell them that wearing the socks inside out can help prevent blisters on the tops of their toes. It is also a good idea for athletes to carry an extra pair of socks to change into if their socks become too damp. A Review Of Helpful Lubricants And Drying Agents When athletes have areas of the feet that are prone to blistering, applying lubricants (like petroleum jelly, bag balm or even dry soap flakes) before they put on socks helps reduce friction. Athletes should reapply large amounts of petroleum jelly every 10 miles during long walks or running events. Instead of petroleum jelly, some athletes prefer applying non-petroleum anti-chafing lubricants, such as BodyGlide (W. Sternoff, LLC) or Runner’s Lube (Mueller Sports Medicine, Inc.), prior to a long distance walk to prevent blisters. These products are waterproof, perspiration-proof, non-greasy, and wash off with soap and water. Another recommendation is to massage both feet with lanolin every night for a month before a big walking or running event. It’s better than petroleum jelly since it doesn’t create heat when friction occurs. It is also a good barrier for water in case it rains during the event. Minimizing moisture on the feet by using drying agents is another way to reduce blister formation. In a double-blind study conducted at the U.S. Military Academy, cadets who used the prescription antiperspirant Drysol (Person & Covey, Inc.) for at least three nights before a 21km hike had a 21 percent incidence of foot blisters, as compared to 48 percent for the placebo group. Drying foot powders, such as Zeasorb (Stiefel Laboratories, Inc.), and antiperspirant sprays (that contain aluminum chlorhydrate or aluminum chloride) are inexpensive ways to decrease moisture. Other Preventive Approaches Toughening the skin is another method of avoiding blister formation. Conditioning the skin by gradually increasing activity tends to lead to the formation of protective calluses rather than blisters. Applying multiple coats of tincture of benzoin to sensitive areas or soaking feet in strongly brewed tea (tannic acid) are commonly used skin toughening procedures. Protecting or “shielding” areas of the foot with a high potential for blister formation is an excellent preventive approach. Some of these susceptible areas include bony prominences such as: The dorsum of hammertoes; medial prominence areas of bunions and tailor’s bunions; the posterior heel; and the middle of the arch, especially when the athlete is using orthoses. Products such as Band-Aid Blister Block (Johnson & Johnson, Skillman, N.J.) and Dr. Scholl’s Cushion Blister Treatment (Schering-Plough Healthcare Products) are self-adhesive, silicone-like pads that act as an extra layer of skin to absorb friction. They are available in various sizes. If athletes apply them properly, these pads can stay on the skin for several days, even through showers. Cut slightly larger than areas of intense friction or sensitive skin, moleskin provides another inexpensive method of preventing blister formation. Liquid adhesives, such as Mastisol (Ferndale Laboratories, Inc.), promote adherence of moleskin to the foot. Alternatives to moleskin are the “liquid” bandages such as New Skin (Medtech Laboratories, Inc.), which dries to form a tough protective covering on the skin. Athletes may also consider using lambswool, commonly used by dancers, between the toes in order to prevent and/or soothe blisters. Pertinent Treatment Tips Since it’s not always possible to prevent blisters, it is important to relieve pain, prevent enlargement or infection, and promote a speedy recovery when they do occur. Small, intact blisters that don’t cause discomfort usually don’t need treatment. The best protection against infection is a blister’s own skin or roof. To protect the roof, you can cover this type of blister with a small adhesive bandage or blister guard. However, you should drain larger or painful blisters that are intact without removing the roof. Proceed to apply an antibiotic ointment and cover it with a bandage. Remind runners to change their dressings daily. If you’re dealing with blisters that have large tears, you should “unroof” them and cleanse the base thoroughly with soap and water or an antibacterial cleanser. Then cover it with an antibiotic ointment and bandage. Additional padding may be necessary for continuing sports activity. Ring-shaped pads made of felt will protect small blisters. Larger blisters may require dressings such as DuoDerm (ConvaTec), Spenco 2nd Skin (Spenco Medical Corporation), Vigilon (CR Bard, Inc.), or Opsite (Smith & Nephew United). Doughnut-shaped paddings may be used in conjunction with these dressings. Dr. Caselli (pictured) is Vice-President of the greater New York Regional Chapter of the American College of Sports Medicine and is a Professor in the Dept. of Orthopedic Sciences at New York College of Podiatric Medicine. Dr. Chen-Vitulli is a podiatric orthopedic resident at the V.A. Hudson Valley Health Care System in Montrose, N.Y.
References 1. Burkhart CG: Skin disorders of the foot in active patients. The Physician and Sportsmedicine, Vol 27, No 2, February 1999. 2. Caselli MA, Longobardi SJ: Lower extremity injuries at the New York City marathon. JAPMA, Vol 87, No 1, January 1997. 3. Ellis J: Between a sock and a hard place. Runners World, Vol 24, No 8, August 1989. 4. Feet first (care and treatment of foot ailments). Chemist & Druggist, Miller Freeman UK Ltd, November 25, 2000. 5. Knapik JJ, Reynolds K: Risk factors for blisters during road marching: Tobacco use, ethnicity, foot type, previous illness, and other factors. Military Medicine, Vol 164, February 1999. 6. Knapik JJ, Reynolds K, Barson J: Influence of an antiperspirant on foot blister incidence during cross-country hiking. J Am Acad Dermatol, Vol 41, No 4, October 1999. 7. Knapic JJ, Reynolds KL, Duplantis KL, Jones BH: Friction blisters. Pathophysiology, prevention, and treatment. Sports Med, Vol 20, No 3, September 1995. 8. Ramsey ML: Avoiding and treating blisters. The Physician and Sportsmedicine, Vol 25, No 12, December 1997. 9. Schwartz SEB: Avoiding the rub. Runners World, Vol 27, No 7, July 1992.