High compression refers to medical compression garments or bandages that apply strong, sustained pressure to your limbs, typically 30 mmHg or above at the ankle. These are prescription-level products used to treat serious venous and lymphatic conditions, as opposed to the lighter compression socks you can buy over the counter for travel or mild swelling. The higher the compression class, the more force the garment exerts on your tissues, and the more specific the medical reason needs to be.
How Compression Classes Work
Compression garments are grouped into classes based on how much pressure they deliver, measured in millimeters of mercury (mmHg). Light compression (Class I) starts around 15 to 20 mmHg and is commonly used for tired, achy legs or minor swelling. Moderate compression (Class II) ranges from roughly 20 to 30 mmHg and treats conditions like mild varicose veins. High compression (Class III) sits at approximately 30 to 40 mmHg, and very high compression (Class IV) exceeds 40 mmHg.
These numbers aren’t universal. Different countries define the classes slightly differently. In the German standard, Class I starts at 18 to 21 mmHg, while the French standard defines light compression as just 10 to 15 mmHg. The English standard places Class I at 14 to 17 mmHg. A stocking classified as Class III (high compression) under the German system might be labeled Class IV (very high compression) under the French system. If you’re comparing products across brands or countries, checking the actual mmHg rating matters more than the class number on the label.
All compression garments deliver the most pressure at the ankle and gradually decrease pressure as they move up the leg. This gradient design is what pushes blood upward toward the heart rather than letting it pool in the lower limbs.
What High Compression Does Inside Your Veins
The core mechanism is straightforward: external pressure narrows your veins. When veins are narrower, blood flows through them faster, which reduces the chance of clotting and pooling. But there’s a more specific effect that makes compression especially useful for venous disease. Many people with chronic vein problems have valves inside their veins that no longer close properly, allowing blood to flow backward (a problem called reflux). Research published in the British Journal of Surgery found that external compression can push the walls of a dilated vein close enough together that the valve leaflets meet again and start functioning. In other words, compression doesn’t just squeeze blood upward. It can actually restore the one-way valve mechanism that keeps blood moving in the right direction.
The pressure needed to fix faulty valves is significantly lower than the pressure needed to completely flatten a vein shut. This is why properly fitted compression works therapeutically without cutting off circulation.
Conditions That Require High Compression
High compression garments are reserved for conditions where moderate pressure isn’t enough to control symptoms or prevent complications. The most common include:
- Chronic venous insufficiency: When vein valves in the legs fail over time, blood pools in the lower legs, causing swelling, skin changes, and eventually ulcers. High compression is often the primary treatment to heal venous leg ulcers and prevent recurrence.
- Lymphedema: A progressive condition where the lymphatic system can’t drain fluid properly, leading to significant swelling. Cancer treatments like surgery and radiation are the leading causes of secondary lymphedema in North America, with breast cancer accounting for the vast majority of cases in clinical trials. The gold standard treatment, called complex decongestive therapy, relies heavily on multi-layer compression bandaging during the intensive reduction phase, followed by daily compression garments during long-term maintenance.
- Deep vein thrombosis (DVT) recovery: After a blood clot in a deep vein, high compression can help manage post-thrombotic syndrome, the chronic swelling and pain that sometimes follows.
- Severe varicose veins: When varicose veins cause significant symptoms or skin damage, higher compression levels may be prescribed alongside or instead of surgical options.
For lymphedema specifically, the treatment unfolds in two distinct phases. The first is an intensive reduction phase involving specialized massage, multi-layer compression bandaging, skin care, and targeted exercises. Once swelling is reduced, you transition to the maintenance phase: wearing a daytime compression garment, continuing skin care, and performing exercises at home. Studies have shown measurable benefit from both self-applied compression bandaging and nighttime compression garments during this second phase.
Who Should Not Use High Compression
High compression is not safe for everyone. The biggest concern is peripheral arterial disease (PAD), where arteries in the legs are already narrowed or blocked. Squeezing an already blood-starved limb with strong compression can cause tissue damage or worsen ischemia. An international consensus statement on compression risks established clear cutoffs: if your systolic ankle pressure is below 60 mmHg, your toe pressure is below 30 mmHg, or your ankle-brachial index (ABI) falls below 0.6, sustained high compression with stockings or elastic bandages is contraindicated.
The ABI is a simple test that compares blood pressure in your ankle to blood pressure in your arm. A value above 0.8 generally means high compression can be applied safely. Between 0.5 and 0.8, only low compression should be used. Below 0.5, compression should be avoided entirely pending specialist evaluation.
Heart failure is the other major concern. Compression pushes fluid from the legs back into the central circulation, which adds volume to an already overloaded heart. Severe heart failure (classified as NYHA Class IV) is a contraindication for compression therapy. Even in moderate heart failure (NYHA Class III), compression garments are not routinely recommended and should only be used under close monitoring when there’s a strong reason.
Putting On High Compression Garments
One of the most common complaints about high compression is simply getting the garments on. Class III and IV stockings are significantly stiffer and tighter than anything you’d find at a pharmacy. Many people need donning aids, which are devices specifically designed to help stretch the garment open so you can slide your limb in. Different designs exist for arm and leg stockings.
A few practical tips make the process easier. Put stockings on first thing in the morning, before your legs have had time to swell. Pull the fabric on in stages rather than trying to yank it up in one motion. Distribute the material evenly to avoid bunching or wrinkling, which can create pressure points. Keep your toenails trimmed and heels smooth to avoid snagging the fabric. Knee-length stockings should sit about two centimeters below the back of the knee, and thigh-length versions should end about two centimeters below the fold of the buttock.
Getting fitted matters enormously at these pressure levels. A garment that’s too tight in one spot or too loose in another won’t deliver the graduated pressure profile it’s supposed to, and could potentially cause harm. Your medical supply store or prescribing clinician should measure your limb at multiple points and demonstrate proper application before you start wearing high compression on your own.