Here's a commonsense guide to avoiding that plague of all athletes: blisters
What's the most common athletic injury? No, in spite of what you may have read elsewhere in SIB, it's not the sore knee, the sprained ankle, plantar fasciitis, the separated shoulder, the blown hamstring, the aching Achilles tendon, or any of a number of other injuries which spring to mind. It's the often-forgotten yet ubiquitous skin blister.
Unfortunately, blisters can form quite easily during athletic activities of all kinds. The basic problem is that your skin is constructed like sedimentary rock - but without any of its toughness. Layers of different types of tissue lie upon each other to form your skin, but these layers can be pulled apart by frictional forces created during activity. It matters not whether the friction is created by the handle of a tennis racket, the oar of a boat, or the inside of a sock or soccer shoe: as the skin layers separate as the result of forces placed on them by external objects, hydrostatic pressure pushes fluid from adjoining tissues into the open spaces between the layers. Cells irritated by the frictional forces and the influx of water send waves of stinging pain to your brain - often to such an extent that the ability to compete may be significantly reduced. Races and tennis matches have been lost because of the sudden appearance of a patch of red-hot, water-laden skin. In these cases, victory goes not necessarily to
the fittest - but to the competitor with the toughest skin.
The ideal skin for blisters
What can you do to prevent blisters from forming? As you think about that, it's important to remember that the chances of developing a blister increase as the forces on the skin become larger or as the frequency of force application increases. In addition, blister formation depends on something called the coefficient of friction, which depends on skin characteristics, the degree to which the skin is moistened, and the presence or absence of lubricating agents ('Friction Blisters: Pathophysiology, Prevention and Treatment,' Sports Medicine, vol. 20(3), 1995).
Somewhat surprisingly, when an object like a racket handle, an oar, or a stocking rubs against moist skin, it produces higher frictional forces than it does when contacting either dry or very wet skin. Dry skin is superior when it comes to friction reduction because when significant forces are applied to dry skin, they tend to quickly tear off the very outer layer of the skin, which is called the stratum corneum. Although that sounds bad, the truth is that the ripped-off cells tend to form a sort of lubricating, free-floating, protective barrier over the remaining skin. It's a bit like sprinkling graphite powder on your epidermis.
At the other end of the spectrum, the excess water on very wet skin forms a barrier between the skin and a frictional surface, whatever it may be, which helps to lower frictional forces. Moist (slightly wet) skin is the true blister culprit, because surface tension created by the thin coating of water holds skin cells together, impedes their movement, and thereby hikes the frictional effect. Thus, one key to blister prevention is to keep your skin as dry as possible. If skin wetness is unavoidable, it's better to have your skin very wet - rather than merely moist.
Thou shalt not lubricate
Of course, many athletes believe it's a good idea to spread lubricating agents over areas of skin vulnerable to blistering - in the belief that these agents can reduce frictional forces on the skin. This idea has been tested thoroughly in the military environment in both the UK and the US, because blisters limit soldier mobility and therefore may be life-threatening. The less-than-sanitary conditions which often prevail in military settings also increase the chances that blisters may progress to more serious conditions such as cellulitis or sepsis. Naturally, military authorities want to decrease the probability of blisters to near-zero.
Many substances have been tested by the armed forces in the hope of reducing skin friction, including mineral oil, propylene glycol, silicone fluids, liquid paraffin, talcum powder (talc), sebum (an oil naturally found in human skin), peanut oil, petroleum jelly, and glycerin. It's logical to think that these substances would work to prevent blisters, since they provide a barrier between the skin and a frictional surface, and they certainly create a perception of less friction when they are applied to the skin. However, research has shown that these products reduce friction for less than an hour. One hour after application, friction forces rise to usual levels again, and three hours after application the friction coefficient is actually 35-per cent greater than usual.
Thus, the research indicates that lubricating agents are effective for only brief periods of time and may actually enhance the possibility of blisters in the long run. In theory, one problem is that these substances hold water in the skin (they very effectively block evaporation of water); as a region of skin becomes a 'holding tank' for water, surface tension increases and there is extra water available to flow into any open spaces which form in the skin. The lesson for athletes is that lubricants like petroleum jelly may lower the risk of blisters during workouts or competitions lasting less than an hour (note, though, that the probability of blistering in such relatively short events is already fairly low). However, lubricants should never be utilised during efforts which last more than an hour.
Athletes sometimes apply antiperspirants to areas of the skin which are prone to blistering, the idea being that reduced sweating should keep the skin relatively dry and lower the incidence of blisters. Anecdotal reports indicate that rowers tend to have fewer blisters on their hands when antiperspirants are applied, and a few case studies have linked antiperspirants with a reduction in blister frequency, but carefully controlled, double-blinded, cross-over studies have indicated that anti-perspirants aren't effective at all, perhaps because the emollients used in the anti-perspirant solutions decrease friction initially but increase it in the long run.
Drying powders seem to make sense, since the powders should soak up moisture and keep the feet or hands dry. However, scientific investigations have shown that as compounds like talcum powder soak up moisture, they actually increase frictional forces on the skin. It's possible that the chemical combination of alkaline sweat and a powder actually creates abrasive surfaces as the powder clumps together. Studies conducted by the British army have usually shown that foot-powder wearers do not have lower frequencies of blisters, compared to powder-free soldiers. In fact, one investigation actually linked the use of foot powder with a higher blister incidence!
Commercially available Spenco insoles which contain closed-cell neoprene are supposed to reduce friction on the undersurface of the foot, and research suggests that they in fact may limit the risk of blistering. In one study, athletes wearing a Spenco insole and a single sock in one shoe and two socks without the insole in the other shoe had a 50-times greater incidence of blisters in the foot without the Spenco insole (however, blistering may have been increased by the presence of two socks, which can enhance foot slippage and apply extra force to the foot in areas in which the second sock 'bunches up').
In a separate study, Spenco insoles were compared with insoles containing a cellular polyurethane substance called Poron during 18 weeks of basic training for US Coast Guard recruits. 33 per cent of recruits with no special insoles developed blisters, versus just 17 per cent with Poron and a very impressive 5 per cent for Spenco wearers. Total injuries (contusions, fasciitis, tibial stress, calluses, and metatarsalgia) were also lower in the Spenco soldiers. Overall, the research revealed that Spenco insoles could help reduce the frequency of blistering and other maladies.
A better kind of sock
Of course, much research has focused on the effects that various kinds of socks have on blistering. Basically, these investigations reveal that acrylic or polyester socks are better than cotton or wool ones. They also show that thick socks maintain their bulk during sweating and compression better than thin socks and thereby absorb more force at the skin surface, reducing blister probability (this is only true, of course, if the thick socks don't make the feet fit too tightly within the shoes).
Footwear is also important. Too-tight shoes increase the force exerted by the shoe on the foot, enhancing blister formation, while too-loose shoes increase foot movement and therefore the frequency of force application, also bolstering blisters.
Somewhat surprisingly, losing weight reduces the frequency of blisters, because the forces placed on feet are lower. Your skin also adapts to repeated stresses over time (the outer layer of the skin actually becomes thicker), reducing your risk of blistering as you become more experienced in your sport. If you doubt this, take a trip to Nairobi in February next year and participate in the Nairobi half-marathon. As you pace along the uneven, glass-and-rock-strewn streets, you'll notice that over half of your fellow runners are competing without any outer coverings on their feet at all, yet these athletes remain blister-free. Their secret? They routinely train in bare feet on rugged ground and build up a stratum corneum as resilient and tough as the hide of a rhinoceros.
Petroleum jelly doesn't seem to work
Athletes who do a lot of running often rely on two other strategies to reduce the risk of foot blisters - the application of a special commercial covering called Moleskin or the placing of petroleum jelly on blister-prone areas of the feet. Research suggests that Moleskin is indeed helpful, because it creates a situation in which frictional forces are applied to the top of the piece of Moleskin, not to the outer layer of skin on the foot. However, petroleum jelly does not appear to be beneficial. As mentioned above, petroleum gels reduce friction initially but may actually enhance frictional forces in the long run.
Basically, if you keep your skin surfaces as dry as possible, if you allow your skin a chance to adapt to frictional forces (by increasing your exercise load gradually), if you wear the correct kind of socks (and perhaps Spenco insoles as well), and if you apply Moleskin to areas of skin which blister easily, you should be able to reduce your risk of blistering to nearly zero - and thereby enhance your chances to train well and achieve competitive success.