Compression Socks

What it is

Compression socks, also called compression stockings or hosiery, are stretchy knee-high or thigh-high garments that squeeze the ankle most and the calf less. Medical versions come in pressure classes: about 18-21 mmHg for class I and 23-32 mmHg for class II, while light support socks apply as little as 8-10 mmHg [1][2]. Trials have tested them during long flights, on long standing shifts and in people with chronic venous insufficiency [3][4][2].

How it might work

Graduated pressure is meant to narrow the leg veins and help blood flow back to the heart instead of pooling while the legs are still. In a 12-month trial of healthcare workers, stocking wearers had a lower venous filling index after each shift [4].

What the research says

Flights. A 2021 Cochrane review pooled 12 randomised trials with 2,918 passengers on flights longer than five hours [3]. In the trials that tested stockings on both legs, 50 of 2,637 passengers with follow-up data developed a symptomless deep vein thrombosis: 3 wore stockings and 47 did not (odds ratio 0.10, 95% confidence interval 0.04 to 0.25; high-certainty evidence). Superficial vein thrombosis was less common with stockings (4 versus 12; odds ratio 0.45, 95% confidence interval 0.18 to 1.13; moderate-certainty evidence), but this difference was not statistically significant. No deaths, pulmonary emboli or symptomatic deep vein thromboses were reported, so those outcomes cannot be assessed. Stockings reduced oedema across six trials (low-certainty evidence) and no significant adverse effects were reported [3].

Two flight trials measured swelling directly: a three-hour flight trial (34 adults, one stocking on one leg) found less ankle and calf swelling on the stocking leg [5], and a trial in 47 pilots and passengers on flights of five hours or more found about 0.19 cm less ankle swelling plus better ratings for pain, discomfort, swelling, energy and alertness [6].

Standing and sitting at work. Four small randomised trials agree. Two medical stockings (18-20 mmHg) and one light-support stocking (8-10 mmHg) all reduced lower-leg volume and leg complaints over days of ordinary activity, with the firmer stockings doing more [1]. In a two-hour standing test, class I and class II stockings both reduced lower-leg oedema in healthy people and in chronic venous insufficiency patients [2]. Healthcare professionals on six-hour standing shifts had decreasing leg volume with stockings and increasing volume without them over 12 months, with better vein symptom scores [4]. Hairdressers had about 19 mL less lower-leg volume and about 12% better pain-and-swelling scores with 15-20 mmHg stockings [7]. An international consensus statement rates compression stockings for venous oedema as supported by moderately robust evidence [8].

Travel context. Air travel is linked to a modest increase in venous thromboembolism risk, and guidelines generally advise no clot prevention for travellers without risk factors and compression stockings, rather than drugs, for those with risk factors [9].

Doses used in studies

Flight trials used graduated stockings worn during the flight, from knee-high to tights [3]; one trial used tights with 5 mmHg at the ankle rising to 17-20 mmHg at the calf [6]. Workplace studies used 8-10 mmHg, 15-20 mmHg and 18-32 mmHg stockings [1][7][2]. Durations ranged from a single flight [5] to 12 months of shifts [4].

Safety and interactions

The flight trials reported no significant adverse effects [3]. Compression is considered unsafe in severe peripheral arterial disease, where leg arteries are narrowed, and in decompensated heart failure [10]; in an expert survey, advanced arterial disease was treated as an absolute contraindication [11]. People with diabetes and nerve damage should take care: a case report described second- and third-degree burns in a man with diabetic neuropathy who wore a copper-containing compression sock in the sun [12]. In pregnancy the evidence is thin: a review of seven small trials (326 women) found too little data on stockings for leg oedema in pregnancy, and no study data were found for breastfeeding [13]. Compression socks are garments, so medicine interactions are not expected, and none were reported in the trials cited here [3]. There is no toxic dose; what differs between products is the pressure applied, from light support at 8-10 mmHg to class II at 23-32 mmHg in the trials cited here [1][2].

Caveats and open questions

The main gap is outcome: no symptomatic clot, lung clot or death occurred in the flight trials, so the effect on those outcomes cannot be assessed, and a trial able to answer that question would need very large numbers [3]. The flight swelling evidence is rated low-certainty because trials measured swelling in different ways [3]. The workplace trials are small (44 to 108 people) and mostly tested healthy workers [2][7][1].