Blister plasters and hydrocolloidal dressings

Last updated: July 22, 2009.

It's a hot summer's day and you've decided to go on a 16-km (10-mile) walk along the coast. You've almost home... when you feel a sudden stabbing pain in your foot. Taking off your shoes and socks, you find the skin has worn through and a blister's forming. What can you do? Struggle on and you'll make it worse with every step. But you're miles from anywhere and there's no other way home. This age-old walker's dilemma has become a lot less of a problem thanks to the development of amazing blister plasters made of hydrocolloids. Not only do they protect the wound and keep it clean, they cushion it and allow it to heal faster by absorbing and wicking away its moisture.

Photo: There are many different brands of hydrocolloidal plasters including these Compeed ones made by Johnson & Johnson. Other well-known brands include Comfeel, Tegasorb, and Hydrocoll. They're easy to find in drug stores (chemist's shops), but you'll also find them in sports and outdoor stores among the walking and hiking supplies. In hospitals, hydrocolloidal wound dressings have been used for treating many types of wounds (including burns, ulcers, and sores) for over 20 years.

What's the stuff inside?

Take the protective layers off a hydrocolloidal blister dressing and you'll see that it looks quite different to a normal plaster. It has a sort of rubbery texture, a bit like a chewy sweet that's been run over by a steamroller. The material you're looking at contains a substance called a hydrocolloid that likes to absorb moisture.

Photo: A Compeed plaster looks much like a normal one when you take it out of the packet. It's only when you apply it to your skin that you find out how differently it works.

A colloid is an evenly spread-out mixture. You've probably heard of emulsions and aerosols, which are two common types of colloid. Milk is an emulsion (a mixture of fat particles in a watery fluid) while smoke (a mixture of soot particles in hot rising air) is an aerosol. "Colloid" is the broad, overall name for substances like aerosols and emulsions where one substance is distributed through another. A hydrocolloid is simply a type of colloid where a substance is mixed with water. Hydrocolloidal substances (such as gelatin) love to absorb water to form a gel.

In a hydrocolloidal plaster, the rubbery stuff contains a gel-forming material such as sodium carboxymethylcellulose (a water-soluble polymer made from cellulose) mixed with gelatin. There's a top layer of elastomer (elastic material) to hold the plaster together, while your body flexes beneath it, and there's some harmless adhesive mixed in so the whole thing sticks to your skin and stays there for at least a few days.

How does a hydrocolloidal wound dressing work?

Photo: A blister on the foot: a moist wound that heals in a few days if you keep it clean and dry—but a real nuisance if you're on a walking holiday. Hydrocolloidal dressings help blisters to heal quickly and hygienically, even if you're out and about. Sorry about the gory photo! It's here in the interest of medical science. I made it as small as I could!

Stick a hydrocolloidal dressing onto your blister and it starts to absorb moisture from the wound (medically, this is referred to as "exudate") to form a gel. That's why a hydrocolloidal blister dressing rapidly turns into a soft and spongy mass that cushions your wound, allowing you to keep on walking. The gel is cohesive, which means whatever leaks from your wound stays in place under the dressing. Initially, the dressing doesn't let water vapor escape. But, over time, it becomes more permeable and the wound gradually dries out and heals beneath it. Unlike with a normal dressing, it's usually possible to remove a hydrocolloidal dressing without damaging the wound beneath. Great news for blister sufferers, because the last thing you want to do is tear newly formed skin.

Tips for using hydrocolloidal dressings

I'm not a physician and I am not offering you definitive medical advice, but here are a few quick tips from my own experience of using hydrocolloidal dressings that you can take or leave as you wish:

• I've found that hydrocolloidal dressings work better on some parts of your foot than others. Unless you're going to keep your foot still, they're less effective on toes and heels than on the wider areas, because they tend to work their way free before the wound is properly healed underneath them. You can stop this happening by applying some tape to the underside of your blister dressing to keep it in place—at least to begin with.
• It's important to choose a blister dressing that's big enough to cover the wound completely and make a perfect seal all around it. If you use one that's too small, you'll find the hydrocolloidal gel starts to leak out under the edges. The wound won't heal, dirt can get in underneath it, and you can easily damage the wound again when you remove the dressing. If you're off walking or hiking, the best thing is to buy (and carry) a little box of dressings of various different sizes: bigger ones for heels, smaller ones for toes.
• Don't try to peel a hydrocolloidal dressing away from the wound until it feels ready to come away all by itself. Remember that the wound and the dressing merge together as the new skin forms. Take the dressing off too soon and you'll take the new skin with it—ouch!— and you'll have to start all over again. So be patient!
• If you're at home and you don't need to move around much for a couple of days, you might well find that a blister heals best simply by leaving your foot open to the air without a dressing of any kind. If you're on a long walk, you can't really leave a blister as it is—unless you want to hobble home in pain. That's exactly when a hydrocolloidal dressing really comes into its own. Apply it properly and it should get you to the end of your walk in complete comfort!