Chapter 6: Your Skin
In this chapter
- Drying strategies
One of the most common rookie mistakes leading to blisters is to start a new type of activity without any thought to adapting your skin. By training in the shoes, socks and other gear, and on the terrain, you allow the skin to adapt to the physical demands of your activity. And this provides a protective function. Research has shown that when the skin is subjected to repeated frictional forces below that which causes blistering, epidermal cell turnover is faster, cells are more resistant to frictional forces and the stratum corneum becomes thicker.¹³ ¹⁴ ²¹ ³⁶ ⁴⁰ These adaptive changes (on mouse ear skin) occur sooner than you might expect – changes after 7 days are identical to those at 14-35 days.¹³ ¹⁴ ³⁶ And it takes approximately 28 days for skin cells to move from the bottom of the epidermis to the surface.³⁶
A level of reduced blister incidence has been reported with:
- having spent more time in the particular shoes³³ ⁵⁷ ¹⁰⁰
- having previous experience in the activity⁸⁵
- with more miles trained per week by runners²¹ ⁴²
Gardner and Hill⁵⁷ found hikers that had not preconditioned their footwear were more likely to get blisters (32.1% versus 25.5%) – a mild protective effect. And in testing double sock systems against standard military issue socks, Thompson³² found reduced blister incidence was most noticeable early on in recruit training, when “recruits are adapting to the rigors of physical training.” Patterson³³ found 95% of blisters to occur in the first three weeks of training with the following distribution, suggesting foot skin may require 2-3 weeks for adaptive changes to occur:
- Week 1: 35%
- Week 2: 51%
- Week 3: 9%
The take home message here is, depending on your blister threshold, although adapting your skin to your activity does not ensure protection from blisters, it will be a step in the right direction and should not be neglected.
But you can take this too far – At its best, the adaptive thickening of the corneum is barely noticeable. At its extreme, it constitutes a callus. Some believe calluses to be protective. While there is no doubt a thicker corneum will reduce the likelihood of abrasions (just because there is more thickness to wear through before getting to raw skin), blisters are not abrasions (as discussed in Chapter 3). And clinical experience suggests that thick calluses are far from protective. In fact, the shear experienced under a thick callus is more likely to be destructive to deeper layers of the skin and make blistering and blood blisters more likely.
Figure 33: Blood blister under a callus
Skin toughening – is a phrase used to describe the effect of some preparations used in blister prevention, like Compound Benzoin Tincture, alcohol, salt water, black tea.²¹ ²⁶ ¹⁰⁵ These preparations more appropriately fit a ‘skin drying strategy’ providing for a lower frictional force – discussed next.
- Skin becomes more resistant to shear when subjected to repeated shear cycles.
- It helps to train in the gear and on the terrain to benefit from this blister protective function.
- Calluses are not protective to blisters.
2) SKIN DRYING STRATEGIES
Moist skin has higher friction than very dry or very wet skin.¹ ³ ¹¹ ¹⁷ ¹⁸ ²⁰ ²² ¹¹⁶ ¹¹⁹ The theory is simple: keeping your skin dry – keeps skin friction low – hopefully below your blister threshold – successful blister prevention is the result. But keeping your feet dry is a tough ask – surrounded by socks, enclosed in shoes, sweat, varying amounts of evaporation, exercise, environmental conditions! Then consider if you sweat more than average. It’s not difficult to see how a ‘very dry’ in-shoe environment might be all but impossible to achieve. Skin drying strategies include:
- Astringent skin treatments (often termed “skin toughening”)
- Moisture-wicking socks (discussed in Chapter 5)
Antiperspirants – Antiperspirants are chemical agents that reduce sweating (spray-on, roll-on or powder form). The most popular antiperspirants have aluminium chloride and aluminium chlorohydrate at varying strengths as the active ingredients.⁶⁹ Aluminium-based antiperspirants work by blocking the sweat ducts, thereby reducing the amount of sweat that reaches the skin’s surface. Sweat continues to be produced by the sweat gland but it isn’t able to reach the surface of the skin.⁶⁹ Based on this, there may be a risk of an intra-epidermal maceration (weakened skin). Aluminium-based antiperspirants have been tested in blister research. The table below summarises the effect on blister incidence but at the expense of skin irritation.
Figure 34: The disappointing results of antiperspirants for blister prevention (Ref 34, 45, 130)
Another antiperspirant, Prantal Powder, works differently. Its active constituent diphemanil methylsulfate effects the parasympathetic nerves that control sweat production, to prevent perspiration altogether.⁶⁹ No research has been performed in relation to blister prevention.
Powders – Talcum powder has the ability to absorb moisture and act as a dry lubricant.¹⁰ ¹⁷ But adding 13-17% hydration (ie: when your feet get a bit sweaty) causes the friction coefficient to increase. “It is self-evident that talcum does not remain dry in such areas as the foot for very long” and “the addition of talc to socks would be expected to increase frictional trauma.”¹⁰ Both Knapik³⁷ and Richie⁸⁸ cite three British military studies from the 1960s that tested the use of drying powders to find either no benefit or an increased blister incidence. If for whatever reason a powder is your blister prevention strategy of choice, frequent reapplication is required and is better than using too much in one application.
‘Skin toughening’ – Skin toughening is a phrase used to describe the effect of some ‘astringent’ preparations used in blister prevention, like Compound Benzoin Tincture, alcohol, salt water, black tea²¹ ²⁶ ¹⁰⁵ but of which there is no blister or skin friction research.³⁷ ⁶⁰ ⁸⁸ An exact ‘skin toughening’ mechanism of action is not clear. Since astringents “precipitate protein, reduce permeability of the cell membrane and reduce transcapillary movement of plasma proteins”⁸¹ this possibly has a drying effect to the outer stratum corneum. If so, this is not so much ‘skin toughening’ but rather a skin drying strategy. More consideration for a blister prevention mechanism is required and research to demonstrate a protective effect to blisters.
- Moist skin exhibits higher friction than dry skin – so keeping skin dry is a method of blister prevention.
- The in-shoe microclimate dictates that the skin is usually moist.
- Neither antiperspirants nor powders have proven to be both safe and effective and there is no data on the use of astringent preparations. Moisture-wicking socks (discussed earlier) have proven to provide a level of blister protection.
At the opposite end of the skin moisture spectrum are lubricants. Vaseline (petrolatum) is a well-known one, you apply it to your foot and friction definitely reduces. El-Shimi¹⁷ and Highley¹⁸ explain that viscous lubricants like this work by forming a film on the skin which keeps your sock and skin apart. Interestingly, the frictional properties have nothing to do with the skin-sock interface but rather, the hydrodynamic properties of the lubricant. Even more interestingly, over time, the lubricant disperses and absorbs and friction actually increases:
- As the lubricant film becomes thinner, the contact increases between the surfaces and the observed friction level is less about the hydrodynamic properties of the lubricant
- The lubricant absorbs into the skin, increasing skin hydration and therefore skin friction
Figure 35: Lubricants are occlusive and gradually increase skin friction – adapted from Malvi (Ref 131)
Landmark research by Nacht²⁰ measured skin friction for 6 hours after using moisturisers graded according to their perceived “greasiness”. The level of greasiness determined whether friction increased or decreased, as outlined in the graph below. Only the very greasy lubricants (petrolatum, heavy mineral oil and glycerin) reduced friction, and only for 60-90 minutes. Highley¹⁸ produced similar results with viscous lubricants and Sivamani et al⁶³ found similar trends for increased skin friction with water and slightly/moderately greasy moisturisers. It should also be noted that the probe that was moved over the skin was a flat non-porous surface. Comaish and Bottoms¹⁰ suggest a reduction in friction will be shorter-term when the skin is in contact with a fabric such as a sock. Perhaps this is why lubricants are applied very liberally.
Figure 36: Change in friction after application of different moisturising / lubricants to the skin – adapted from Nacht and Wolfram (Ref 20, 22)
The increase in friction found by these researchers is what Richie⁸⁸ eludes to when he states “Physicians, coaches and athletic trainers continue to advocate the use of petrolatum jelly and skin powders to prevent blisters while the scientific literature suggests these measures may actually increase the chance of blistering on the feet.” The potential limitations to the use of lubricants include:
- Initial lack of traction – Lubricating large areas of the feet, particularly the weightbearing sole of the foot may not be a good idea. In preventing blisters, it is not the aim to reduce friction indiscriminately. A targeted approach is the ideal approach so that traction and functional efficiency are maintained.
- Later friction increase – This won’t be a problem with short duration exercise but for longer duration efforts, you would need to reapply the lubricant to maintain any benefit. If not, not only has your blister protection gone, you’re actually at more risk of blistering.
- It weakens the skin – Lubricants have an occlusive effect that traps moisture within the skin. By reducing transepidermal moisture loss, skin hydration is excessive and prolonged. In other words, the skin becomes water-logged. And water-logged skin is weaker and less able to resist trauma.³³ It’s a bit like how your skin goes when you’re in the bath for too long.
- Attracting grit & messy – The common lubricant Vaseline (petrolatum jelly) can be a poor choice, particularly on off-road surfaces as it has a tendency to attract grit. And its potential carcinogenic properties have attracted some attention recent times as it is a product of petroleum. Viscous lubricants like Vaseline are messy too.
- Lubricants affect friction at the skin-sock interface.
- Moisturisers and less greasy lubricants increase friction.
- Viscous lubricants initially reduce friction. As the lubricant absorbs and dissipates, friction increases.
Figure 26: Coefficient of friction data in dry and moist conditions – adapted from Payette (Ref 125)
- Cushioning materials reduce peak pressure by spreading load over a larger area.
- Cushioning materials can also absorb shear via their shear modulus.
- More cushioning is not always better as it can affect shoe fit and reduce functional efficiency.
Sports tape applied to blister susceptible areas is a common prevention strategy. Leukoplast, Fixomul, KinesioTex Tape and RockTape are popular choices and there are many others. And blister dressings like Compeed are also popular. These products are adhered to the skin.
By admission from athletes, sports medicine professionals and manufacturers themselves, taping provides protection from rubbing. Rubbing removes skin cells from the skin surface to progressively deeper and deeper layers causing abrasions. But this is not blister prevention – because you don’t need rubbing to cause blisters.¹² ⁴⁸ ⁷³ ⁹⁴ This describes abrasion prevention. So how does taping prevent blisters? Surprisingly, there is a lack of evidence.³⁷ ⁶⁰ ⁸⁸ And a proposed mechanism of action has not attracted significant discussion in the literature either (other than is stops rubbing – which misses the crux of blister causation). Actually, rubbing will cause some shear, but not as much as when there is no rubbing¹⁰ ²⁴ ⁹⁴ (Chapter 2 figure 6).
So tapes and dressings may help reduce blister formation, if the tape’s surface provides lower friction than skin friction. Understanding this, Polliack and Scheinberg⁷⁰ gathered a number of blister dressings and tested their friction properties (table below). The over-riding impression from this research is that most of these coefficient of friction values are very high, when compared to the values shown in the graphs from Carlson⁵⁶ and Payette¹²⁵ in Chapter 5 figure 28 & 29.
Figure 37: Coefficient of friction data of blister dressings – Adapted from Polliack and Sheinberg (Ref 70)
Unfortunately, there is no such coefficient of friction data for tape, neither from research nor their manufacturers. So we don’t know whether individual tapes reduce friction or not! Knapik³⁷ confirms plain adhesive tape can be used to prevent rubbing (ie: abrasions) “and may be effective if it reduces the coefficient of friction (ie: if it is ‘slick’).” Of taping, Richie⁸⁸ states “There are no published studies to show these measures actually work. Few things applied to the feet will stay intact for more than one hour of vigorous activity” highlighting the effect of perspiration and the extreme in-shoe conditions that are constant threats to adhesion.
An alternative mechanism of action – Although not described in the literature, it is plausible that tapes reduce shear at discrete locations due to the fact that they’re adhered to the skin. Just as cushioning spreads the vertical load over a larger area to reduce peak pressure, because tape is adhered to the skin, does tape spread the ‘pull’ of the horizontal load over a larger area to reduce peak shear distortion per unit area of skin? In other words, by spreading the shear load, shear per unit area of skin will be less (Carlson, 2013: personal communication).
Taping technique – Whatever the mechanism of action, the success of taping relies on keeping the tape well-adhered to the skin. Much effort is put into perfecting both the choice of tape and the application technique. Yet there is little consensus on either.
John Vonhof¹⁰⁵ ¹⁰⁸ is arguably one of the most accomplished practitioners of taping for the most extreme of ultramarathon conditions- from dry desert to tropical jungle environments. He favours the kinesiology tape called StrengthTape in wet conditions. Other taping advice from Vonhof, particularly in maximising adhesion include:
- Compound Benzoin Tincture applied to the skin before taping in order to maximise adhesion.
- Apply tape at least one hour before use (if not the night before) which allows the tape’s adhesive time to bond with the skin.
- Rub the tape for 20-30 seconds after applying it to the skin – it warms the adhesive to make it more tacky.
- When using kinesiology tapes, lay the tape on the skin and if you have to stretch the tape around a heel or toe, only apply a slight stretch. The more stretch you apply, the more likely the tape is to come loose, especially in wet conditions.
- It takes as long as it takes – a precision tape job can take more than 30 minutes. Practice makes perfect and an adequate application technique can take time.
Figure 38: Vonhof’s taping technique
- Anna Beetham for Oxfam Trailwalker in Melbourne uses Fixomul and explains her application technique in this video: https://youtu.be/dIHILzTQ8ek. Trent Salkovich prefers Leukoplast and uses the following technique: https://youtu.be/hHxLjumvd0M.
- There has been very little research on how taping prevents blisters.
- Tapes and dressings prevent abrasions.
- Perspiration compromises the adhesion of tapes and dressings.