Blister plasters and hydrocolloidal dressings

Last updated: May 20, 2008.

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 one of your shoes has worn the skin right 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 plaster and you'll see that it looks quite different to a normal wound dressing. 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.

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 something like 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 it work?

Photo: A blister on the foot: a moist wound that heals in a few days if you keep it clean and dry. Hydrocolloidal plasters help with both these things.

Stick a hydrocolloidal plaster 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 plaster 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 plaster without damaging the wound beneath. Great news for blister sufferers, because the last thing you want to do is tear newly formed skin when you remove your plaster.

A word of advice

Photo: Hydrocolloidal plasters stick firmly and should stay in place for several days. You can usually see the wound healing through the surface.

I'm no doctor, but my own experience is that hydrocolloidal blister plasters 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 wide areas, because they tend to work their way free before the wound is properly healed underneath them. It's also important to choose a plaster that's big enough to cover the wound completely and make a perfect seal all around it. If you use a plaster 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 plaster. If you're off 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.