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Invited Commentary

Exploring the Mechanism for Blister Prevention Using Moleskin

Rushton, Rebecca J. BSc(Pod)

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Current Sports Medicine Reports: November 2020 - Volume 19 - Issue 11 - p 451-453
doi: 10.1249/JSR.0000000000000768
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Abstract

An Introduction to Moleskin

Moleskin is a heavy, durable cotton fabric with a velvety knap on one side and an adhesive on the other. It is one of the most commonly used tools for prevention and treatment of blisters, used by athletes and recommended by doctors (Fig. 1). However, it is our opinion that moleskin is often incorrectly used. This is because of a fundamental misunderstanding of moleskin's protective mechanism. Most users and prescribers of moleskin assume that it reduces friction. However, it is our professional opinion that moleskin may actually increase friction levels.

Figure 1
Figure 1:
Moleskin applied to the back of the heel for the purpose of blister prevention.

The cotton that moleskin is made of would seem to be an inferior material for reducing friction — a common refrain in blister avoidance is to avoid cotton socks. Because cotton is a hydrophilic material, any foot perspiration or other moisture is easily absorbed and retained by cotton, further increasing friction levels, whether in socks or in moleskin.

Further unpacking this conundrum, some exploration of the cause of blistering is in order. We have no disagreement that moleskin prevents abrasive rubbing of the skin (e.g., protection against dirt or sand in the shoe). However, abrasive rubbing of this kind on the skin surface does not cause blisters — it causes abrasions, which are a superficial-to-deep wear injury to the skin. In marked contrast, blisters are an intraepidermal fatigue injury caused by repetitive shear distortions.

In considering friction in the context of moleskin, it can be defined as the resistance to the movement of one surface across another. High friction levels yield more resistance, whereas low friction levels yield less resistance. High friction levels cause higher shear distortions within the skin, which is the ultimate cause of blisters. Low friction levels cause low shear distortions and, therefore, reduced chance of blisters (Fig. 2). So, it would seem that adding moleskin to a blister or a blister-prone area on the foot would actually increase friction, by substituting the skin-sock interface with a cotton fabric-sock interface. And moving outward, the sock-shoe interface has not been changed, so friction remains the same there. How then does moleskin deliver any blister protection? The academic research community unfortunately has not compared the physics of blister prevention methods as thoroughly as we would like, but there are several published studies that directly explore this question.

Figure 2
Figure 2:
A depiction of shear distortion within soft tissue, adapted from Hoffman (1). The friction force between the skin and footwear opposes the movement force, creating shear distortion within the adjacent soft tissue.

Polliack and Scheinberg (2) compared the coefficients of friction of various types of blister dressings in dry conditions. The second and third lowest measured coefficients of friction in their study are brands of moleskin (Fig. 3).

Figure 3
Figure 3:
Coefficient of friction data of blister treatment products from Polliack and Scheinberg (2).

However, Carlson (3) did similar experiments with materials used in the orthotics and prosthetics profession, comparing coefficients of friction both when dry and wet. While moleskin was comparable in friction levels to several other treatments when dry, when wet, it has the highest coefficient of friction of all treatments tested (Fig. 4).

Figure 4
Figure 4:
Coefficient of friction data of materials used in the orthotics and prosthetics profession in dry and wet conditions from Carlson (3).

We often use two other products featured in Figure 4 for blister prevention: Poron (Rogers Corporation, Rogers, CT) and ShearBan (Tamarack Habilitation Technologies, Blaine, MN). Poron is a common cushioning material used by podiatrists for many interventions including blister prevention. Compared with moleskin, its friction properties are slightly more favorable. The other material we use from the above figure for blister prevention is called ShearBan, also known as Engo Blister Patches. This is an effective friction-reduction material that we provide to many patients, customers, and use ourselves. It is effective for active people for blister prevention and for patients with foot ulcers.

Clearly, there are multiple products that more effectively reduce friction when compared with moleskin — especially once moisture is introduced.

How Does Moleskin Protect against Blisters?

Despite the clear evidence against moleskin as a significant friction reducer, there is no doubt moleskin provides relief for some people's hot spots and blisters. If not from friction reduction, from where does this relief derive?

It is our professional opinion that moleskin works by spreading shear load across a larger area of skin, similar to the mechanism of athletic tape. In fact, we believe it is accurate to refer to moleskin as a type of thick, cotton tape. Instead of the shear distortions in the skin being confined to the localized blister-susceptible area, moleskin works by spreading shear stress over the entire area to which the moleskin is applied, thereby reducing the absolute shear stress and potential damage to any individual spot. Reinforcing this point, a critical part of moleskin application is to apply it to an area substantially larger than the blister area itself. More rigid moleskin also provides greater blister protection, because this also results in spreading shear load more evenly. There are a wide variety of brands of moleskin with variable rigidity. Selection should be performed balancing maximal rigidity versus likelihood of effective fixation given the shape and contour of the affected area. For example, more flexible moleskin does not provide the highest shear load spreading but is optimal for foot areas with complex shapes like bunions or toes. This mechanism by which tapes like moleskin spreads shear stress to prevent blisters was first described in 2013 by Rushton (4) and later by Hoffman (1) and Rushton (5).

Alternative Approaches for Using Moleskin to Treat Blisters

Moleskin also is commonly used to treat blisters using another approach known as donut pads. A central space is cut out of a larger section of moleskin to be placed over the affected area. The protective mechanism in this instance is not a reduction of friction levels but a reduction of pressure within the central space. However, based on our own decades of practice in podiatry, the thickness of a single layer of moleskin is insufficient to provide significant pressure relief to any foot blister when fashioned as a donut pad. Even a double layer of moleskin is not sufficiently thick. It takes a much thicker donut pad to deflect pressure by this means, using a material like orthopedic felt (6–9). Our professional recommendations are a thickness of 7 mm. Curran et al. (7) have shown that 7-mm deflective padding performs significantly better than 5-mm deflective padding at reducing peak pressure. The average thickness of moleskin is approximately 2 mm.

Conclusions

We hope this has been a sufficient illustration to suggest that the mechanism by which moleskin prevents blisters is not by reducing friction, but by spreading shear load across a larger surface area of skin. Few have made this observation, and it is an area ripe for further academic investigation and greater acceptance among podiatrists and sports medicine practitioners. While there are alternative friction management materials superior to moleskin, recognition of moleskin's protective mechanism may pave the way for investigations, such as comparing the coefficients of friction of the many tapes used in blister prevention or comparing rates of blister formation with tapes of the same coefficient of friction but with differing rigidity.

The author discloses that she is a distributor for Tamarack HTI’s ShearBan/ENGO products in Australia.

References

1. Hoffman MD. Etiological foundation for practical strategies to prevent exercise-related foot blisters. Curr. Sports Med. Rep. 2016; 15:330–5.
2. Polliack AA, Scheinberg S. A new technology for reducing shear and friction forces on the skin: implications for blister care in the wilderness setting. Wilderness Environ Med. 2006; 17:109–19. Available from: http://dx.doi.org/10.1580/PR30-05.1.
3. Carlson JM. Functional limitations from pain caused by repetitive loading on the skin: a review and discussion for practitioners, with new data for limiting friction loads. J. Prosthetics Orthot. 2006; 18:93–103.
4. Rushton R. Taping. In: The Advanced Guide to Blister Prevention. 1st ed. 2013. [Internet]. Available from: https://blisterprevention.com.au/advanced-guide-to-blister-prevention/.
5. Rushton R. Tape use to prevent blisters: does it really do what we think it does? Lower Extremity Magazine. 2019. Available from: https://lermagazine.com/article/tape-use-to-prevent-blisters-does-it-really-do-what-we-think-it-does.
6. Raspovic A, Waller K, Wong WM. The effectiveness of felt padding for offloading diabetes-related foot ulcers, at baseline and after one week of wear. Diabetes Res Clin Pract. 2016; 121:166–72. Available from: http://dx.doi.org/10.1016/j.diabres.2016.09.018.
7. Curran MJ, Ratcliffe C, Campbell J. A comparison of types and thicknesses of adhesive felt padding in the reduction of peak plantar pressure of the foot: a case report. J. Med. Case Rep. 2015; 9:203. Available from: http://dx.doi.org/10.1186/s13256-015-0675-8.
8. Nieto-Gil MP, Ortega-Avila AB, Pardo-Rios M, Gijon-Nogueron G. Effectiveness and duration of plantar pressure off-loading by two designs of felt padding: a preliminary study. J. Am. Podiatr. Med. Assoc. 2019; 109:431–6.
9. Zimny S, Reinsch B, Schatz H, Pfohl M. Effects of felted foam on plantar pressures in the treatment of neuropathic diabetic foot ulcers. Diabetes Care. 2001; 24:2153–4.
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