Robert Rinaldi, DPM
Posted January 8th, 2011
More than 400,000 athletes participate in marathons every year. In the shorter distances, participation is well into the millions. All this running, just in the United States! Training miles for these runners must be an awesome figure.
The injury most frequently treated in running race medical tents is the painful friction blister. Consider these statistics:
•An estimated 39 percent of runners experience disability from blistering feet during a race.
•The United States military records show blister treatment for over 40 percent of all inductees in training.
•An estimated 50 percent of hikers and backpackers suffer from blisters.
•The friction blister is common, painful, and disabling, yet prevention and treatment are still fixed on a paradigm of traditions that was set more than 30 years ago.
With blisters, pain may be the most minor of problems. Blisters can become infected, leading to sepsis, cellulites, and even toxic shock. With a high potential for serious complication it is a wonder that more attention has not been placed on prevention. Understanding the process of formation may debunk some long-standing myths about blister treatment.
The blister begins with a tearing of the top three layers of the skin—stratum corneum, stratum lucidum, and stratum granulosum—from the underlying stratum spinosum. The skin’s lowest basal cell layer and dermis remain unharmed. The space created from the tear fills with a “blister fluid’ that is very similar to plasma. The original tear is caused by a shearing force or frictional force that develops between the skin and an object that has less mobility and greater tensile strength. Once the plasma-like fluid fills the space it will actually begin to add insult to injury by further dissecting tissue as it moves about, making the blister larger.
Frictional forces are important in the process of movement and for the foot to work normally. These forces will help develop stability and traction, working with the enormous amount of neuro-receptors on the plantar aspect of the human foot. Frictional force will increase with heat or moisture. Exercise will increase metabolic activity and cause heat build-up. Studies have shown that as little as a four-degree increase in heat will increase blister formation by 50 percent. Skin temperature on the plantar aspect of the foot will increase by six degrees with just plain walking. That said, understanding the reason for formation of the friction blister has offered little help in the prevention of blisters.
Debunking old wives’ tales
Folk medicine lore is replete with tips and tricks for the prevention of the friction blister. Sadly, most of the remedies have been shown to offer little help in resolving the dilemma. Exhaustive studies performed by the U. S. Army have shown that applying an antiperspirant to the sole of the foot not only did not prevent blistering, but added the possibility of an allergic skin response to the products used.
Another popular blister prevention trick is to use a moisture-absorbing powder, such as cornstarch. A premium-grade baby powder was most popular, but studies found that the talc or cornstarch absorbed moisture and also the sharp edges of the particles, which would further irritate the skin, resulting in the formation of a blister.
Finally, the use of lubricants such as petroleum jelly, K-Y Jelly, and a product that was marketed as Unpetroleum Jelly were tested. The results showed that in most cases the formation of the blister was increased.
Shoes and socks
The solution for blister prevention might be found in footwear. Think of the shoe as a glove on your foot. If the glove is too large it will be cumbersome and give your hand only fumbling protection. Work will be out of the question since all dexterity will be lost. Conversely, if the glove is too tight it will constrict blood flow, impinge nerve endings, and generally be very uncomfortable.
So it is with a shoe. A shoe that is too loose will increase the chances of blisters, since the foot will move about inside the shoe. At heel-strike the foot will begin its slide forward and at toe-off the shoe will begin a track backwards. As the skin warms up and moisture increases, the foot will literally be sloshing around in the shoe. When the shoe is too tight it will increase friction on the skin almost immediately. The shoe must fit properly; it can be neither too tight nor too loose.
I always suggest that you shop for your athletic foot wear in a quality sport shop with trained staff. We are blessed here in Vermont with Skirack in Burlington, Onion River Sports in Montpelier, and Stateline Sports in West Lebanon, NH. You could not find better staff to meet your fit needs.
The final answer to blister prevention may be in the socks. Studies have shown that acrylic fibers are best, blowing cotton fibers out of the running. High-grade acrylic fiber with minimal underfoot padding combined with shoe insoles constructed with closed cell neoprene fiber such as Spenco has shown to reduce blistering as much as 25 percent.
Close to nothing is worse than a blister in the long run. Though there is no cure nor prevention, the next best thing is to use athletic shoes that are appropriate for your foot type, and control hyperpronation if necessary. Equally important—use thin, high-grade acrylic socks.
If you get a blister it is best to stop your activity. Leaving the fluid in the blister will cause it to get larger in a process called fluid dissection, so I recommend opening the blister in several places, allowing it to drain, then apply Betadine solution to help prevent infection. Betadine also acts as a drying, dehydrating solution. Finally, do not cover the wound with a bandage, so it can dry and heal.
Robert Rinaldi is a board-certified podiatrist and podiatric surgeon at the Gifford Medical Center in Randolph, VT. He is a fellow and a founding member of the American Academy of Podiatric Sports Medicine, and a podiatric consultant to the Dartmouth College track and cross-country teams. He is a former nationally ranked long-distance runner, having competed in 25 world-class marathons. You can reach him at Gifford Sports Medicine and Surgery Clinics in Randolph, VT, or at the Sharon Health Clinic in Sharon, VT, 802-728-2490 or 802-763-8000 or at firstname.lastname@example.org.