Many of us have had to deal with uncomfortable occurrences of blisters and sores. When they form, your skin can feel extremely sensitive and may even rub away, leaving an open wound. A day of walking in a new pair of shoes can leave the skin on your heels red, raw, and painful. A person who uses a brace or a prosthetic limb may find rub areas on the skin underneath the device. Sitting in a wheelchair or lying in bed for extended periods of time (such as in bed rest) can cause serious sores. These sores can become life-threatening ulcers that penetrate bones or internal organs. Sores are usually treated by reducing pressure, but another often ignored component of treatment is something called friction management. Pressure relief is extremely useful in treating sores, but by managing friction as well, you could experience freedom from hot spots and sores
What does friction have to do with it? Not much, according to the conventional wisdom, which identifies pressure as the cause of sores. In fact, bed sores are commonly referred to as “pressure sores.” This name is all too accurate; too much pressure on one area of the skin can reduce blood flow, cutting off the supply of nutrients and oxygen to the cells there.
But that’s not the whole story. The other force that works with pressure to cause sores is friction. When two surfaces rub or press together, like your sock and the skin on your foot, friction resists the motion. The friction creates something called shear stress on the skin. Shear stresses occur between skin and soft tissues like muscle and fat, and this stress can damage underlying biological supports and weaken skin. While pressure alone can sometimes be enough to cause a sore, the presence of shear stress greatly reduces the amount of pressure needed to cause damage.
Where skin experiences high or repeated friction force and walking (as opposed to pressure sores) are caused almost entirely by friction. Bony areas are high friction areas and are often most subject to skin damage, since there is less soft tissue for cushioning and that tissue is subject to more shear stress.
It’s important to mention that not all friction is bad. Friction helps us grip the ground as we walk, and it helps keep us seated in our chairs. The problem arises when an area of skin is subject to too much friction and/or shear. For instance, people who use a transfer board to slide in and out of a wheelchair will be subject to a great deal of friction where they rub against the board, even through clothing. Weakened skin also increases problems. People who have received skin grafts may find that their skin is less elastic and more fragile. People with diabetes sometimes face nervous system damage and decreased pain sensitivity, which can mean that they only notice sores after they have become severe. Moisture also increases friction. One common way for this to happen is for sweat to build up. You might think that applying lotion could reduce friction, and though lotion initially lubricates the skin and reduces friction, it soon spreads too far and is absorbed into the skin. This creates a moist, even “sticky” surface.
One way to manage friction and shear is to put a layer of low-friction material between the sore and the part of the shoe, brace, seat, etc. that is irritating the skin. This immediately reduces friction force on the sore and gives the skin time to heal. If you’re susceptible to blisters or sores, remember that pressure-relieving remedies help, but they ignore half of the equation. Reducing friction could make all the difference.