An Unna boot is a paste-impregnated gauze bandage wrapped from the toes to just below the knee, providing both wound healing support and compression for venous leg ulcers. The technique relies on specific foot positioning, a pleating method to accommodate swelling, and a secondary outer layer to hold everything in place. Getting it right matters: applied too tightly, it can cut off circulation; too loosely, it won’t provide the compression needed to heal the ulcer.
What an Unna Boot Is Made Of
The original formula, developed by dermatologist Paul Gerson Unna in 1885, is gauze impregnated with 15% zinc oxide in a glycerin-and-gelatin-based paste. Zinc oxide promotes healing and soothes inflamed skin, while the paste stiffens as it dries to create a semi-rigid compression layer around the lower leg. Modern versions sometimes substitute calamine for zinc oxide, but the basic concept is the same: a moist, medicated bandage that hardens into a supportive boot.
Unna boots are primarily used for chronic venous ulcers, the slow-healing wounds that develop when blood pools in the lower legs due to poor vein function. They’re also sometimes used for stubborn skin conditions on the extremities, including certain types of eczema and thickened, itchy patches caused by repeated scratching.
Before You Start: Wound and Skin Prep
Clean the skin thoroughly before applying the bandage. If there’s an open wound, a primary dressing goes on first. Typically this means a thin contact layer (a non-stick mesh) placed directly over the ulcer, sometimes with a hydrogel to keep the wound bed moist. This protects the wound from sticking to the paste bandage and makes removal less painful at the next change.
One critical safety check should happen before any compression bandage goes on: confirming that the blood supply to the leg is adequate. If the arteries in the leg are severely narrowed, compression can dangerously reduce blood flow to the foot. An ankle-brachial index (ABI) reading below 0.6 is a clear contraindication. This is a simple, painless test that compares blood pressure at the ankle to blood pressure in the arm, and it should be done before starting Unna boot therapy.
Step-by-Step Application
Positioning the Foot
Have the patient sit or lie with the foot supported off the floor. Position the foot in dorsiflexion, meaning the toes are pulled up toward the shin so the ankle sits at roughly a 90-degree angle. This ensures a comfortable walking position once the boot dries and stiffens. If the foot is wrapped while pointed downward, the hardened boot will lock the ankle in that position and make walking difficult.
Wrapping the Foot and Ankle
Start at the base of the toes. Using no tension, wrap the paste bandage around the foot with about 50% overlap on each pass, meaning half of the previous layer is always covered by the next. Work around the foot, over the heel, and up around the ankle, making sure every surface is covered with no gaps of exposed skin. The key here is zero tension. The paste bandage has no stretch to it, and pulling it tight at this stage can create dangerous pressure points.
Wrapping Up the Leg With Pleats
Once you reach above the ankle, the shape of the leg changes from a narrow ankle to a wider calf. Because the paste bandage has no elasticity, it can’t conform to this widening shape on its own. This is where the fanfold technique comes in.
With each turn up the leg, fold the bandage back on itself just off-center of the front (anterior) surface of the shin. These small pleats, sometimes called fanfolds, create a row running up the front of the leg. They serve two purposes: they let the bandage lie flat against a leg that’s getting wider as you go up, and they give the boot a small amount of expansion room if the leg swells. Without pleats, the stiff bandage would either bunch up or become dangerously tight as fluid shifts throughout the day.
Continue wrapping with 50% overlap and consistent pleats until you reach just below the knee. Avoid wrapping over the knee itself, as this would restrict bending.
Applying the Outer Layer
The paste bandage alone isn’t the finished product. A secondary coverage layer goes over the top. This is typically a dry, conforming gauze wrap (sometimes called a kling bandage) or a self-adherent elastic wrap. The outer layer serves a few roles: it holds the paste bandage securely in place, adds a degree of additional compression, absorbs any drainage that seeps through, and keeps the sticky paste from catching on clothing or bedding.
How Long the Boot Stays On
An Unna boot is typically changed every three to seven days. The exact timing depends on how much fluid the wound is producing and how much the leg is swelling. A wound with heavy drainage may soak through the boot in just a few days, requiring an earlier change. A drier wound with minimal swelling can go the full seven days. Between changes, the boot needs to stay dry. In the shower, wrapping the leg in plastic or a waterproof cover will protect it.
Walking is encouraged while wearing an Unna boot. In fact, that’s part of how it works. As the calf muscles contract during walking, they push against the semi-rigid boot, which pushes back against the leg. This pumping action helps move pooled blood upward out of the lower leg, directly addressing the underlying cause of venous ulcers.
Warning Signs to Watch For
Because the boot stiffens after application, changes in leg size can turn a well-applied boot into a problem. Watch for these signs that something is wrong:
- Tingling, numbness, or color changes in the toes. This suggests the boot is compressing too tightly and restricting blood flow. The boot should be removed promptly.
- Pain in the foot or leg while walking. Some snugness is normal, but actual pain is not. This also warrants removal.
- Swelling above or below the boot. If fluid is being trapped rather than managed, the compression may be causing more harm than good.
- Itching and warmth under the boot. This could signal an allergic reaction to the paste or a developing skin infection.
- Drainage soaking through the boot. The wound is producing more fluid than the dressing can handle, and the boot needs to be changed early.
- The boot feeling very tight or very loose after walking. Either scenario means the fit has shifted and needs reassessment.
Any of the first four signs on that list, particularly toe color changes or new pain, call for removing the boot and getting the leg evaluated before reapplying.
Common Mistakes That Affect Results
The most frequent error is applying the paste bandage with too much tension. Because the material has no give, even moderate pulling during application can create a tourniquet effect once the patient stands and gravity increases fluid pressure in the leg. The bandage should be guided around the leg, not stretched.
Skipping the pleats is another common problem. Without them, the bandage bunches and folds unevenly as it tries to conform to the widening calf, creating ridges that dig into the skin. Those pressure ridges can cause new wounds on already fragile skin.
Wrapping with less than 50% overlap leaves gaps where the paste doesn’t contact the skin, reducing both the therapeutic effect of the zinc oxide and the evenness of compression. Conversely, wrapping with too much overlap creates areas of double or triple thickness that apply uneven pressure.
Finally, positioning the foot incorrectly during application is a mistake that compounds over time. A boot applied with the foot pointed down will fight the patient’s natural gait for every step they take over the next week, causing discomfort, skin irritation, and reduced compliance with treatment.