Podiatry FOCUS

Friction foot blisters: a review of the risk factors, treatment and prevention Farina Hashmi

The skin of the foot is susceptible to developing a range of mechanical dermatoses as a consequence of the repetitive loads generated during walking and running.The friction blister is included in this class of conditions and is not to be underestimated, as blisters can be painful, become infected and alter gait patterns leading to abnormal loading and resultant foot and ankle damage or overuse injuries (Bush et al, 2000).This article will look at the physiology of blister creation, risk factors associated with blisters, and prevention and treatment options. Incidence Friction blisters present in people of all ages and activity levels but those at increased risk are runners (Brennan, 2002; Mailler-Savage, Adams, 2006), hikers (Kogut, Rodewald, 1994), those wearing incorrect footwear or hosiery (Dai et al, 2006) and the military (Patterson, Leister, 1980; Knapik, Hamlet, 1996). The sites most commonly affected by friction blisters are the toes, the heel and the plantar surface of the foot.

a.

b.

The physiology of blister creation Friction blisters are specific to the palmoplantar skin (Basler et al, 2004) due to its unique structure, in particular thicker stratum corneum, compared to skin elsewhere on the body (Akers, Sulzberger, 1972; Akers, 1977). The thick epidermis is firmly held down by the dermis, therefore minimising the movement of the epidermis across the dermis and consequently reducing the effects of shear. When the external shear forces exceed the binding forces of the skin, a cleft forms between the stratum granulosum and stratum spinosum epidermal layers (Sulzberger et al, 1966; Akers, Sulzberger, 1972; Akers, 1977), which gradually fills with

Dr Farina Hashmi, PhD, FCPodMed, is a Research Fellow at the School of Health, Sport and Rehabilitation Sciences, University of Salford

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Risk factors associated with friction blisters Figure 1a. Friction blister on the posterior aspect of the heel generated under laboratory conditions. 1b. Ultrasound image confirming the architecture of the blister. tissue fluid. Researchers have recorded the clinical signs and symptoms as a friction blister forms on the posterior aspect of the heel (Hashmi et al, 2013). Initial shear application causes exfoliation of the most superficial layers of the stratum corneum and

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then the skin appears to redden. With continued rubbing a small pale area develops in the centre of the ‘hot spot’ and it is at this point that the individual feels a burning or stinging sensation. Eventually the pale area of skin elevates allowing for the tissue fluid to occupy the area gradually (Figure 1). The pain caused by the blister is due to the trauma experienced by the skin as well as the accumulation of fluid in a relatively small area. Hydrostatic pressure influences the ingress of fluid into the blister, therefore if the blood supply to the skin is compromised in anyway the pressure reduces and less fluid moves into the intraepidermal cleft. Dawson et al (2004) classified the stages of development of a blister to aid the diagnosis and management of each specific stage (Figure 2). There are many factors that can place foot skin at increased risk of blistering. Some have already been mentioned; however there are many others that are summarised briefly below. The risk factors for blistering can be divided into two categories: 1) Intrinsic factors, which refer to systems associated with the body that alter the structure and function of skin, and 2) Extrinsic factors, referring to changes in the environment that can influence the behaviour of skin. www.bdng.org.uk

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Podiatry FOCUS determine whether foot structure and mobility is compromised in such a way that excessive pressures are generated at specific points on the foot. Some chronic diseases affect body position and mobility, which could result in increased plantar pressure loading (Sanders et al, 1995).

Stage 1 Hot spot

Pain and skin irritation

Stage 2 Intact fluid-filled blister

Stages 3a & b a: Collapsed blister b: Collapsed blister

Reddened base convered by an intact blister roof Red and painful with a denuded blister roof

Figure 2. Stages of blister development (Dawson et al, 2004). Skin moisture Skin moisture can be considered to be both an intrinsic and extrinsic risk factor for blistering. Epidermal moisture can influence the mechanical behaviour of skin and can also alter the frictional forces generated between the skin surface and the contact materials (eg, socks). Moist skin is more susceptible to friction blistering (Akers, 1977; Bush et al, 2000), primarily because the coefficient of friction is higher in moist skin compared to dry or excessively wet skin (Naylor, 1955; Highley et al,1977). In the case of there being an excess amount of moisture on the skin, the fluid acts as a lubricant and when the skin is relatively dry, the exfoliated layers of stratum corneum cells form a powder that also has a lubricating effect. With this in mind, feet that tend not to sweat excessively, such as those of the elderly and children, are less likely to be at risk. However, it must be noted that other changes in an aging foot, as a consequence of peripheral vascular disease and systemic disease, make the skin susceptible to physical trauma and breakdown. Changes in environmental conditions, such as humidity and temperature, particularly within the shoe, influence the moisture of the skin. High temperatures and sweat accumulation lead to increased skin irritation during running (Hennig et al, 2005). Therefore, the appropriate choice of footwear, socks and topical preventative therapies is imperative for young adults who are prone to having sweaty feet and blistering. There will be more on treatment and prevention options later on in this article.

Intrinsic factors Data collected from people after specific army training activities show the rate of incidence of blister to be three times greater in females compared to males (Patterson, Leister, 1980; Patterson, et al 1994). It is not clear why this difference exists. One possible explanation could be that males have a thicker epidermis compared to females (Sandby-Moller et al, 2003), however this inference comes from data collected from skin sites on the upper body and not the feet. Patterson et al (1980, 1994) also noted from their military training studies that Caucasian skin showed a higher risk of blistering than black skin. Some researchers have gone as far as to suggest that different sock materials should be used by the two different skin types, ie, nylon socks by fairskinned people and a cotton athletic sock by black-skinned people, however there is little scientific evidence to support this recommendation. Due to the painful nature of a friction blister, sufferers may be inclined to alter the way they walk to offload the painful area, therefore increasing the risk of musculoskeletal foot and ankle injuries (Bush et a, 2000). Altered gait may also subject other skin sites to extraordinarily high pressures, therefore compounding the problem further and causing more blisters to form elsewhere. If an individual experiences repeated episodes of blistering after taking part in a specific type of activity, it would be wise to conduct a biomechanical assessment to

Extrinsic risk factors Poorly fitting footwear appears to be a key factor that contributes to blister creation, however the only published works in this area originate from military exercise studies (Bush et al, 2000). No research to date has been carried out on different types of footwear and their contribution to blistering. However, more work in the area of socks and friction has been conducted. As the socks are in direct contact with the skin it is generally agreed that sock fibres contribute to the reduction of shear forces when in contact with foot skin (Herring, Richie, 1990). The primary action of socks is the reduction of friction force by wicking moisture away from the skin surface (Knapik, Hamlet, 1996). A cotton sock has a greater capacity to hold water compared to an acrylic or polyester sock after running (Herring, Richie, 1990). The fibres in a cotton sock swell as the moisture is absorbed. Once the fibres become saturated by fluid, the wicking effect is reduced therefore causing an increase in moisture on the surface of the skin and consequently increasing the risk of blistering (Herring, Richie, 1990; Baussan et al, 2010). This fundamental knowledge supports the need for a sock comprising a material that should not only allow moisture to move away from the surface of the skin but also provide a constant, low coefficient of friction when in contact with it.

Blister prevention and treatment options The preventative measures for friction blisters reported in the literature focus on the reduction of friction and shear forces, and the prevention or removal of moisture from the surface of the skin. These measures range from footcare advice to the use of lubrication and antiperspirants in addition to appropriate socks, insoles and footwear.

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Podiatry FOCUS Foot-care advice In the case of people who lead active lives and are prone to blistering, the first line of action should be footcare advice, focusing on informing the individual of the effective preventative measures that can be taken. Bush et al (2000) observed fewer repeated incidences of blistering in patients who attended clinical appointments for footcare advice. Bush further hypothesised that foot-care advice at the beginning of basic training may result in fewer friction blisters. Lubrication Friction forces on the skin surface can be reduced by the application of a lubricant (Naylor, 1955). Despite the ability of mineral oils to hydrate the skin, via occlusion, they also provide lubrication to the skin. The lubricating effect is thought to overcome the increased friction generated by hydration (Highley et al, 1977). However, this beneficial effect is short-lived as constant rubbing by an external stimulus may cause the film barrier to be removed, leaving the underlying hydrated skin exposed to the same external stimulus. This has led to the development of relatively effective lubricating balms, which generally contain hydrogenated vegetable fat, petrolatum or caprylic triglyceride (an oil substitute). The majority of these products work well in preventing skin chafing on the torso in runners. The evidence regarding efficacy of these treatments in preventing foot blisters is yet to be obtained.

reducing sweat production on the surface of the skin. The true effect of these products only manifests after a few days of use prior to taking part in a specific activity; for example Knapik et al (1998) conducted a double-blind study on a group of 667 military cadets where half were instructed to apply an antiperspirant to their feet daily for 6 days before a 21km hike. The other half (controls) was asked to do the same with a placebo. The results showed that the incidence of blister was low in those who had applied antiperspirant for 3 or more days compared to the controls. However, there was a high incidence of skin irritation reported (57%). The active ingredient in the majority of antiperspirants is aluminium chlorohydrate (also used in deodorants), which reduces the production of perspiration. There are many foot preparations on the market that are made up of this ingredient. Socks The best types of socks that will reduce the risk of blistering are generally made of synthetic fibres such as acrylic (Herring, Richie, 1990; Brenda, 1991) or polyester (Knapik, Hamlet, 1996; Van Tiggelen et al, 2009). These materials are desirable because they reduce friction and keep the foot dry. Recent innovations have led to the production of specific anti-blister socks, which are not only made from low friction fabrics but they also have a double layer composition which dissipates the shear forces, generated by external factors, before they reach the skin surface.

An alternative method of lubrication is dry lubrication. The use of a powder such as Zeasorb (Steifel laboratories Inc, Coral Gables, Florida) has been shown to be effective in the prevention of friction blisters (Basler et al, 2004). There are many blister prevention powders on the market, ranging from loose powder to compact powder sticks and of which the main base component is talcum powder. The sticks are more ‘user friendly’ as the loose powders tend to cling to surfaces including clothes.

Insoles and shoes Insoles and orthotics are not typically used in the management of blisters; however the insole could be an area for further exploration as it interfaces between the shoe and the foot. Although it has been identified that insoles made from a cushioning material absorb vertical forces on compression, it is not known whether specific insole material and design can reduce shear forces.

Antiperspirants Antiperspirant use is aimed at

The correct shoe fit can reduce the likelihood of blister formation but

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it is not clear what constitutes wellfitting footwear in this context. It is known that some shoes increase the risk of developing a friction blister, ie, a military boot is more likely to cause a blister than a running shoe. However, it has also been reported that wearing a military boot before basic military training can provide protection from blistering (Patterson et al, 1994). Plasters and bandages Plasters and bandages can be used to both treat and prevent blisters. The BursaTek bandage (SAM Medical, Tualatin, OR, USA) is the only bandage that has been tested for efficacy in blister prevention. The design of the bandage comprises a dome-shaped material that has the properties of a bursa, therefore absorbing friction. When compared to a range of blister prevention bandages (11 in total) the BursaTek bandage had the lowest coefficient of friction when in contact with the skin (Polliack, Scheinberg, 2006). In another study, Bursatek bandages were randomly applied to sites on the foot on a military 16km hike. None of the skin sites developed blisters (Sian-Wei Tan et al, 2008). Hydrogel and hydrocolloid plasters are widely used in blister management. These plasters can be used to prevent friction damage to the skin and to treat an existing blister with a formed or denuded blister roof (Figure 2, Stages 3a and 3b). The hydrocolloids and hydrogels provide an optimum woundhealing environment and also help to relieve pain and cushion the blister (Read, 2001). The most well-known hydrocolloid plaster is Compeed. Hydrocolloids have slightly different material properties to hydrogels; however the two types of materials are effective in treating and preventing blisters. Hydrogel products are cheaper to manufacture than hydrocolloids and therefore provide a cost-effective alternative for some patients.

Treatment of blisters Most blisters heal naturally and do not require medical attention. As new skin grows beneath the blister, the fluid contained within it will be slowly www.bdng.org.uk

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Podiatry FOCUS a.

b.

c.

d.

Figure 2. Blister protection pad made from semi-compressed felt padding material. Remember to bevel the edges of the pad before applying to the foot (c), this is comfortable for the patient and also prevents the edges rolling away from the skin. Image (d) shows the pad on the posterior aspect of a heel without a blister. The blistered skin should sit within the cavity. reabsorbed and the skin on top will dry and peel off. This process normally takes 3-7 days. The unbroken skin over a blister provides a natural barrier to infection. This means that blisters should remain intact and unbroken. The blister should not be pierced, but should be allowed to break on its own once the skin underneath has healed. According to the information on the Feet For Life website (http://www. scpod.org/foot-health/common-footproblems/blisters/), it is recommended that the blister is protected by foam or felt material of a thickness of www.bdng.org.uk

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approximately 1.5 to 2cm. A cavity should be cut in the pad, forming a ‘doughnut’ shape where the blister will sit. The pad should then be secured with tape or a soft gel-type dressing (Figure 3). If the blister bursts, the skin that forms the roof of the blister should not be removed. The area should be gently pressed to disperse all the fluid inside. It is ideal for this to be done while the foot is in warm water with either salt or soap dissolved in it. The area should then be covered with a

dry, sterile dressing and redressed daily until the skin has healed. Monitoring the healing of blisters in patients who are par ticularly ‘at risk’ (eg, people with peripheral ischemia, neuropathy, compromised immunity, etc) is vital due to the increased risk of infection. Blood blisters should also be left to heal naturally. As with other blisters, if a blood blister bursts it is impor tant to keep the area clean and dry, and protect it with a sterile dressing to prevent infection.

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Podiatry FOCUS Summary Friction foot blisters are a common problem often causing pain and infection, the consequences of which can have a detrimental impact on the quality of life of the individuals involved. As practitioners we are armed with sufficient evidence to provide comprehensive advice regarding the prevention and treatment of blisters. Although more scientific evidence is needed with regards to intervention efficacy, there are many useful measures that can be put in place to protect the foot from such damage. DN

A double-blind study. J Am Podiatr Med Assoc 80(2): 63-71 Highley DR, Coomey M, DenBeste M, et al (1977) Frictional properties of the skin. J Invest Dermatol 69(3): 303-305 Knapik J, Hamlet M (1996) Influence of boot sock systems on frequency and severity of foot blisters. Military Med 161(10): 594598 Knapik JJ, Reynolds K, Barson J (1998) Influence of an antiperspirant on foot blister incidence during cross-country hiking. J Am Acad Dermatol 39(2): 202-206 Kogut K, Rodewald L (1994) A field survey of the emergency preparedness of wilderness hikers. J Wilderness Med 5(2): 171-178

References

Mailler-Savage EA, Adams BB (2006) Skin manifestations of running. J Am Acad Dermatol 55(2): 290-301

Akers W (1977) Sulzberger on friction blistering. Int J Dermatol 16(5): 369-372

Naylor P (1955) Experimental friction blisters. Br J Dermatol 67(10): 327-342

Akers W, Sulzberger M (1972) The friction blister. Military Med 137(1): 1-7

Patterson J, Leister A (1980) The incidence of skin disease in cadets during basic training. Military Med 145(2): 101-3

Basler RS, Hunzeker CM, Garcia MA (2004) Athletic skin injuries: combating pressure and friction. Phys Sports Med 32(5): 33-40 Baussan E, Bueno MA, Rossi RM, et al (2010) Experiments and modelling of skinknitted fabric friction. Wear 268(9-10): 1103-1110 Benda C (1991) Stepping into the right sock. Phys Sports Med 19(12): 125-128 Bush RA, Brodine SK, Schaffer RA (2000) The association of blisters with musculoskeletal injuries in male marine recruits. J Am Podiatr Med Assoc 90(4): 194198 Dai XQ, Li Y, Zhang M, Cheung JT (2006) Effect of sock on biomechanical responses for foot during walking. Clin Biomechan 21: 314-321 Dawson CA, Bancells RL, Ebel B, Bergfeld WF, McFarland EG (2004) Treatment of friction blisters in professional baseball players. Int J Athlet Ther Train 9(3): 62-65 Hashmi F, Richards BS, Forghany S, Hatton AL, Nester CJ (2013) The formation of friction blisters on the foot: the development of a laboratory-based blister creation model. Skin Res Technol 19(1): e479-89. doi: 10.1111/j.16000846.2012.00669.x. Epub 2012 Aug 14 Hennig EM, Sterzing T, Kroiher J (2005) The influence of sock construction on foot climate in running shoes. Footwear Biomechanics Symposium, Footwear Biomechanics Group (International Society of Biomechanics), Cleveland, OH Herring KM, Richie DH (1990) Friction blisters and sock fiber composition.

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Patterson H, Woolley T, Lednar W (1994) Foot blister risk factors in an ROTC summer camp population. Military Med 159(2): 130-135 Polliack A, Scheinberg S (2006) A new technology for reducing shear and friction forces on the skin: Implications for blister care in the wilderness setting. Wilderness Environ Med 17: 109-119 Read S (2001) Treatment of a heel blister caused by pressure and friction. Br J Nurs 10(1): 10-19 Sandby-Moller J, Poulsen T, Wulf HC (2003) Epidermal thickness at different body sites: relationship to age, gender, pigmentation, blood content, skin type and smoking habits. Acta Derm Venereol 83(6): 410-413 Sanders JE, Goldstein BS, Leotta DF (1995) Skin response to mechanical stress: Adaptation rather than breakdown — A review of the literature. J Rehab Res Dev 32(3): 214-226 Sian-Wei Tan S, Kok SK, Lim JK (2008) Efficacy of a new blister prevention plaster under tropical conditions. Wilderness Environ Med 19(2): 77-81 Sulzberger M, Cortese Jr TA, Fishman L, Wiley HS (1966) Studies on blisters produced by friction. J Invest Dermatol 47: 456-465 Van Tiggelen D, Wickes S, Coorevits, P, Dumalin M, Witvrouw E (2009) Sock systems to prevent foot blisters and the impact on overuse injuries of the knee joint. Military Med 174(2): 183-189

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