Blister Prevention

Most runners should not get blisters. There are those who are running in situations that make blisters very hard to avoid Badwater but for distances of 50 miles or less, blisters should not be an issue. I suffer from a skin condition called Epidermolysis Bullosa that makes my skin blister easily, so if I can run 100+ miles without blisters, you should be able to! There are a number of approaches to preventing blisters.

1 Causes of blisters

Blisters are primarily caused by shearing force, which is where force is applied to the skin across its surface. Blisters can also be formed due to trauma, such as stubbing your foot.

Sheering force causing a blister

1.1 Exacerbating factors – Heat & Moisture

Neither heat nor moisture will cause blisters, but they will make them more likely as they both tend to weaken the structure of the skin. If the skin is wet for long enough it will macerate, which sometimes called 'prune skin'. Macerated skin tends to wrinkle up, become white, quite soft and is far more likely to blister.

2 Preventing blisters

There are several key steps to preventing blisters.

2.1 Running form

Bad running form will not only make you slow and cause injury, but it is also a leading cause of blisters. With a good Cadence and running form, your feet will land gently and quietly on the ground, producing little shearing force or impact. A slow Cadence or a poor running form will produce a sharp shearing force that will tear at the skin, causing blisters over time. Running downhill can make the shearing forces far worse, and a poor downhill running style is likely to cause serious blisters. When running downhill, your foot should land softly and the braking force should be even for the time the foot is in contact.

Without paw-back, the foot is still moving forward at the time of contact, creating shearing force

Correct paw-back brings the foot backward in relation to the body, so that it touches down without any forward motion.

2.2 Shoe Fit

A badly fitting shoe can cause blisters even with good Cadence and running form. When buying shoes, try them on when your feet are warm, preferably at the end of the day, and with the socks you will run in. You should generally choose your socks, and then buy your shoes to fit with those socks. Some socks are available in a variety of thicknesses, so you can tweak the fit with different socks.

2.2.1 Loose Shoes

Your foot will slide around in a loose shoe and the pressure will tend to be in small areas, focusing the friction and shearing forces in hot spots. One test of shoe fit is to put your shoes on, but leave the laces completely loose and see if you can walk around without your heel coming out. A good fit will have the shoe fitting gently against your foot, but without any area of higher pressure or pinching.

2.2.1.1 Changes in foot size

Remember that losing or gaining body fat can change the size of your feet. Shoes that used to fit you perfectly may not longer fit the same. A more acute problem occurs on longer races when the feet swell up. Having spare shoes that are slightly larger, or thinner socks for later in a race can help with this problem. Of course, getting the fit right is hard, as you can't practice this until your feet are swollen, and different situations may produce differing levels of swelling.

2.2.2 Inflexible Shoes

An inflexible shoe will tend to pull away from your heal when you’re running, causing problems at the back of your heal. A good running shoe should be flexible and allow you to run with a natural form. I would recommend against trying to fix your running form with shoes, as this approach generally involves attempting to create a compensatory imbalance.

2.2.3 Arch Support

The arch is a naturally strong structure, but arches are damaged by forces pushing up under their middles. This is particularly true of the arches of your feet; they are strongest when there is nothing pushing up under the arch. However, if you've worn shoes that push up under the arch for some time, this will weaken the arch. This is similar to having a limb in a cast; the cast supports the limb, but the limb weakens quickly. Therefore when you try to move to a shoe without arch support, it can be like taking a cast off a limb. Your foot will take time to strengthen and recover from using arch support. The other downside to arch support is the pressure can easily cause blisters. This is especially true of orthotics.

2.2.4 Toe Box

Ideally, the toe box of your shoes should be big enough that your toes can’t touch the sides or top of the shoe. If the toe box is slightly too small, it is easy to cut away the material to prevent contact. I generally leave a bridge of material from the very front of the shoe to near the laces to keep the sole from flopping around too much and just cut away the sides of the toe box.

My Modified Nike Frees with the toe box opened out

2.3 Insole Edge

It is possible for the edge of the insole to cause a blister, though this is fairly rare unless the insole moves within the shoe.

2.3.1 Shoe quality

A bad seam or excess glue can cause a sharp edge that could tear up your skin. A shoe can fit correctly, but cause blisters due to manufacturing problems such as a bad seam. A shoe that bends in the wrong place can have a crease that causes a blister as well. Also, check that your insoles do not slip. Some double sided sticky tape between the shoe and the insole can prevent this.

2.4 Socks

Even the best socks will not prevent blisters if you have bad running form or bad shoes. However, a bad sock will cause blisters on its own; it’s vital to avoid cotton socks, or cheap socks not made for running. If you are on a tight budget, try to get a sock with seamless construction and good wicking (moisture transport) properties such as Coolmax. See Blister Prevention and Socks for more details.

2.5 Hydration

Dehydration can be a contributor to blisters, as the skin loses some of its tension (skin turgor) with significant dehydration. However, reduction in skin turgor is generally associated with 6-9% dehydration (excluding glycogen depletion water losses), at which point the dehydration itself should be more of a problem than the blisters. Hyponatremia is a dangerous condition and one of the symptoms is swelling of the hands and feet, which can cause black toenails or blisters. Read up on Practical Hydration and Hydration 101.

2.6 Calluses

Calluses are a sign of poor fitting shoes. A callus is a spot that is likely to turn into a blister with longer distances. You can file down a callus and keep is moisturized, but that is a symptomatic approach. The key is to fix the underlying problem, which is normally the fit of your shoes. Note that a callus is a spot that is thickening; the general thickening of the skin due to being barefoot does not tend to cause this problem. The key is to watch out for small areas or spots that have excessively thick skin.

3 Desperate Measures

I consider the following techniques ‘desperate measures’, as I believe they are as likely to cause problems as they are to solve them. (Note that DryMax socks should not be used with lubricants or powders, as they will damage the water repelling properties of these socks.)

3.1 Lubricants

A lubricant will reduce the friction between your skin and your socks, which can help reduce the shearing forces, and thus the blisters in some situations. However, most lubricants will also keep your feet warmer and by keeping your sweat against your skin, make the skin wetter. This added heat and moisture will soften the skin and make the chance of blisters greater overall. In cold conditions, smothering your feet in Vaseline can work well, as the added warmth is actually an advantage. Also remember that lubricating your feet can cause a problem if you do get blisters and want to tape them, as the lubricant makes it harder for the tape to stick. Wiping your feet with paper towels, then with paper towels soaked in rubbing alcohol can remove most of the lubricant, but that process takes time to do properly.

3.1.1 Types of Lubricants

Here is a partial list of some of the options

Hydropel helps prevent the skin absorbing moisture and is particularly useful in wet conditions. It does lubricate slightly, but its water repelling powers are its prime attraction.
SportsShield is similar to Hydropel, both being based on a silicone lubricant (dimethicone). SportsShield is available as a roll on and towelette, whereas Hydropel is dispensed from a toothpaste like tube. SportsShield goes on much easier than Hydropel and results in less friction, but less water repelling as well.
Vaseline is cheap and can be used in large quantities. This can provide good lubrication, but tends to keep the skin quite moist. It also makes it harder to attach tape if this is required later.
Aquaphor is quite similar to Vaseline. Though it has different ingredients, I have not found a significant practical difference as a foot lubricant.
Bodyglide is one of the original products purposefully marketed as a sports lubricant. While effective, it does not seem to last very well, nor does it reduce the friction as much as other products.

3.2 Powders

Like lubricants, powders can reduce the friction between your feet and your socks. While powders do not keep your feet warmer or wetter in the way lubricants do, the powder does tend to clump up when damp. These clumps of powder can then lead to blisters.

3.2.1 Types of Powders

Here is a partial list of some of the options

Blister Shield powder is Teflon, which I found helps a bit, but tends to form clumps when wet.
Zeasorb powder absorbs six times its weight in water, which sounds effective, but water is heavy and powder is light. To absorb the level of sweat put out by a runner, a lot of powder is required, which I've found to be impractical.

See Powders and Lubricants.

3.3 Taping

Like the other desperate measures, taping can reduce the friction between your sock and your feet. Unlike lubricants and powders, taping can help absorb some of the shearing force, though this depends on the particular tape used. A flexible tape will just transmit the shearing force to your skin, but an inflexible tape can absorb and spread the shearing force. There are several downsides to taping

Taping will keep your skin warmer and wetter. This depends on the tape, but thicker tapes and tapes that are waterproof are worse. Duct tape is especially bad and will cause the underlying skin to become saturated as it holds the sweat against the skin.
The tape can crease, causing ridges that create extra pressure and blisters. Again, duct tape is particularly bad for this.
If the tape works loose, it can bunch up and cause a blister. Occasionally the tape can migrate around your foot and cause a blister in an unexpected and unpleasant new area.
Should you get a blister under the tape, it can be quite painful to remove the tape to determine the extent of the problem. (I’ve seen a number of cases where are runner was convinced they had a blister, but the skin was fine.)

For more details see Taping.