Most people think that blisters form from friction and rubbing directly on the skin surface, but in fact, blisters are caused by the skin stretching too much. So it’s a shearing force rather than a rubbing one.

When skin is repeatedly stretched too far, tiny tears form underneath the skin surface, and this is the start of a blister. The area starts to fill with fluid in an attempt to repair and protect the area, but if the rubbing continues the skin gets damaged, the blister bursts and the skin is open to infection causing the bushwalker mild to severe discomfort (depending on where the blister is located).

Shear forces are different to rubbing forces because they occur beneath the skin.

Rebecca Rushton has an elegant example of what skin shear feels like:

“Place the tip of your right index finger on the back of your left hand. Wobble it back and forth but keep it stuck to the same bit of skin. Notice how your skin stretches? This is shear and this is what causes blisters.”

Skin is made up of several layers, similar to several layers of plastic. A shear force occurs when the layers move in different directions (or at different speeds). If the shear force is big enough then it will break the joins between the skin. The blister then forms as the body repairs the area by pumping fluid into the injured area, and since there is no material holding the layers together the skin balloons out.

On a bushwalk, feet are usually held tightly in place in footwear by frictional forces between the skin, sock and shoe and lacing. When walking, on every step that contacts the ground, the outer skin of the foot sticks but the other layers move. This creates a shear force on the skin and if the skin is repeatedly stretched further than its natural elasticity, blisters form.

So to reduce blisters we need to reduce shear forces within the skin. Some people are more susceptible to blisters than others. Rebecca Rushton suggests there are four requirements:

1. Skin resilience: everyone has a different level of shear strength in their skin and it varies across the body depending on skin thickness. In general, thicker skin is more likely to form blisters because it’s less mobile, and that’s why blisters tend to form on feet where the skin tends to be thicker.

2. A high friction microclimate: in a sweaty shoe heat and moisture increase friction in an already high friction environment. If this friction can be reduced, so are the shear forces and the likelihood of getting blisters. Therefore, using techniques to reduce friction is crucial to avoiding blisters.

3. Internal structure: the further the inner layers of skin move relative to the outer skin the more likely blisters are to form. Foot bones move quite a lot under the skin. Changing the biomechanics – the structure and function of the body – can lead to immediate blister prevention. These are some of the factors that vary from person to person.

4. How often blisters form: repetitions are how many steps you take. Each step imparts a shear distortion to the skin, so the more steps, the more likely shear damage occurs. Hence, the longer your walk, the more likely you are to be troubled with blisters. Also relevant to this point – the heavier your pack, the more challenging the terrain etc, the sooner the skin integrity will fail, leading to blister formation.

There are a variety of different techniques that can be used to tackle blisters. Each has their pros and cons. Try a variety of techniques to find out what works best.

The right footwear
The most straightforward way of preventing blisters is to make sure that footwear fits well. Well-fitting footwear will be most comfortable and enjoyable to walk in. Minor adjustments to a shoe fit can be made using different lacing techniques. However, some people with well-fitting shoes can still be susceptible to blisters.

Walking in wet footwear increases friction between the shoe and the skin, making walkers far more blister prone. Carry a separate pair of sandals for river crossings and make sure to dry your feet well before putting walking footwear back on.

The right socks
It’s not friction between the skin and the shoe that causes blisters, but rather the rubbing between the various layers of skin (i.e. shearing forces between skin layers). This occurs when there is high friction between the skin and sock. Reducing this friction reduces the shear forces between skin layers.

Moisture on the skin increases friction on the skin. Standard socks absorb some moisture to prevent this, but when exercising, they become saturated quickly. Socks that wick moisture away from the skin may help prevent blisters. Moisture evaporates through the footwear surface until the sock material is saturated, and then the limiting factor is how fast moisture can escape from the footwear. Sometimes this is very slow. Cotton is considered to be the worst material for endurance activity clothing because it keeps moisture trapped against the skin – just the environment for blisters. Acrylic and polyester are effective wicking materials and dry quickly.

Some people find that using two layers of socks are an effective way of reducing the friction between sock and skin, however, the sort of materials and wicking properties are important to get right here. In some cases, using a single sock layer is more effective. You might find moisture-wicking socks, double-socks or toe-socks help you prevent blisters.

Reducing friction
As well as good socks and removing moisture from the skin, there are other ways to reduce friction. Some of these methods include:
- Tape: taping up the blister-prone area before starting the walk can be an effective way of preventing blisters for some people, although it’s a time-consuming process, with variable results.
- ENGO Blister Prevention Patches are made of Polytetrafluoroethylene (PTFE), an ultra-low friction material. They are applied to the insole of the shoe to reduce friction in common blister-prone areas. They’re fast to apply and long lasting but don’t work well when waterlogged.
- Lubricants: care should be taken using lubricants, as research has found that greasy lubricants don’t last long (60-90 minutes), while others actually increase friction. Use with caution!

New footwear or socks take some time to get used to, and blisters may form during the breaking in process. Alternatively, maybe something happened on the trip that was different – a river crossing and wetter feet than normal. Hotspots are the first warning signs of a blister forming. They’re much easier to treat than full blisters, but if ignored will turn into a blister.

Here are some strategies on how to recognise and deal with hotspots and blisters in the bush.

Hotspots are red sores that appear on the skin in an area which has been or is being irritated and are often the first warning sign of an impending blister. That is, there’s still time to prevent it. Stop and take the time to sort it out before it gets any worse. It’s tempting just to push on, but a short stop and a quick fix will most likely prevent a blister forming.

Apply blister prevention strategies. On a bushwalk, the easiest ways to treat hotspots include: taping with Fixomull, Elastoplast or Moleskin.

The best way to treat a blister depends on how much of the blister roof is still intact. The roof is defined as the top of the blister, and could be intact, torn or deroofed, meaning that the upper skin is complete, partially broken or completely missing. Broken skin makes the skin more prone to infection, and given that feet are in a moist warm environment, they are more prone to infection.

The aim of blister treatment is to stop them happening, and if they occur, avoid infection, reduce pain, and speed up healing.

Intact
Intact blisters are prone to popping once footwear is put on again, so they need to be dressed carefully to reduce the risk of future tearing. Because it is likely to tear skin when removed, don’t put anything sticky on the blister. Use an island dressing, which has strong adhesive on the outside of the bandage and gauze in the middle. Reduce friction, and pressure on the area (e.g. if possible, use different lacing techniques to reduce pressure around the blister) and monitor in case the blister roof tears.

Lancing a blister is to prick or cut open. Whether or not to lance depends on where the blister is located, what the activity is, the health of the patient and what equipment is available. In theory, bushwalkers cannot keep a wound clean enough to justify lancing the blister in the field. However, in practice, many bushwalkers find that with appropriate antiseptic and dressing that the blister does not get infected. Moral of the story: lance with caution and use an antiseptic when the fluid is drained.

Broken
A blister with a broken roof is prone to infection, and first aid treatment must be given to reduce the chance of infection. Put antiseptic on the wound (e.g. Betadine) and follow the same steps as for unbroken blisters and monitor for infection.

Deroofed
When the entire roof of the blister is missing, the wound is prone to infection and the underlying skin needs protection as it is delicate and sensitive. The skin will also weep, so the wound should be protected with a hydrocolloid dressing, which allows healing skin without sticking to it. Follow the same steps as for broken blisters, with a hydrocolloid dressing (e.g. Compeed) instead.