Compression Socks for Flying: Do Flight Socks Really Work?

Flight socks work for the thing they were tested on and have never been shown to work for the thing most people buy them for. Randomised trials of airline passengers show a large drop in symptomless clots and less leg swelling. The same trials recorded no cases at all of a clot that caused symptoms, a pulmonary embolism or a death, in either group, so they cannot tell you whether compression socks prevent those. That gap is the honest answer, and the rest of this page is what sits on either side of it.

I fly a lot and I did not use to wear them, because most of my flights are short European hops. That changed when my gynaecologist told me I should. I take the combined pill, several months in a row, to skip periods, which is one of several ways to make periods easier to deal with while travelling. It also raises the chance of a clot slightly, and her advice was to wear compression socks on anything over three hours, which in my case includes plenty of flights inside Europe. I ordered a pair, I have worn them on long flights ever since, and I am more relaxed on a long-haul than I used to be.

I am not a doctor and none of this is medical advice. What follows is what the published evidence says, what the NHS and the UK’s national travel health service actually advise, and how to buy a pair that fits. If you have had a clot before, or you think you have one now, that is a conversation with a doctor rather than with a travel blog.

Do compression socks actually work on a plane?

Compression socks work on a plane in the sense that they measurably change what happens in your legs, and the size of that change is well documented. The Cochrane review of compression stockings for airline passengers, updated in 2016, pooled 10 randomised trials covering 2,871 passengers on flights of more than four hours. It graded the evidence on symptomless deep vein thrombosis as high quality and found a large reduction: from roughly 10 to 30 cases per 1,000 passengers without stockings, down to 1 to 3 per 1,000 with them.

Two other findings came out of the same review. Superficial vein thrombosis, a clot in a vein near the surface, appeared in 4 passengers wearing stockings and 12 not wearing them, which the review graded as moderate-quality evidence of a reduction. Leg swelling was lower in the stockings group, graded low quality only because the trials measured swelling in inconsistent ways. No trial reported a significant adverse effect, and the reviewers described the stockings as well tolerated.

What the review could not answer is the question people actually ask. Across all 10 trials there were zero cases of symptomatic DVT, zero pulmonary embolisms and zero deaths, in either group. Nobody has run a trial large enough to show whether fewer symptomless clots translates into fewer clots that hurt you, and the reviewers say so plainly. Guidance bodies still recommend compression socks for higher-risk travellers, which is a judgement made on the strength of the indirect evidence rather than on a trial result.

What compression socks do and do not do

Compression socks change blood flow and swelling in the lower leg, and that is the whole of the tested claim. The table below sets each common claim against what the evidence actually supports.

The socks themselves are simple. They are made of stretchy fabric that hugs the foot, ankle and calf, and they are graduated, which means the pressure is highest at the ankle and eases as the sock goes up your leg. That gradient is the mechanism: it helps push blood back up towards the heart when gravity and sitting still are working against it. You do not need a prescription to buy a pair. If you travel often and have a medical reason to wear them, it is worth asking whether your health insurance covers prescribed ones, which is something I did not think to check.

Who should wear flight socks?

Travellers with an added reason to worry about clots are the group every guideline points at, not everyone who boards a plane. TravelHealthPro, run by the UK’s National Travel Health Network and Centre, advises travellers at increased risk of venous thromboembolism to consider properly fitted below-knee graduated compression socks. Its advice for everyone else on a long journey is to move: walk when you can, flex and extend your ankles regularly, keep hand luggage out from under the seat so your legs are free, and avoid tight clothing round the waist and legs.

The NHS lists the things that make a clot more likely. They are set out below.

• Age: being over 60.
• Weight and smoking: living with overweight or obesity, and smoking.
• History: having had a DVT before, or having thrombophilia, a condition where blood clots more easily.
• Medication: taking HRT, or the combined contraceptive pill or another oestrogen-containing contraceptive such as the patch or the vaginal ring.
• Other conditions: cancer, heart failure, varicose veins, inflammatory bowel disease or vasculitis.
• Recent events: a hospital stay, surgery, three or more days confined to bed, pregnancy or the six weeks after giving birth, and dehydration.

Pregnancy gets a firmer recommendation than the rest. TravelHealthPro says pregnant travellers on flights of more than four hours should have graduated compression socks fitted, and the word doing the work there is fitted, not bought. If you are pregnant and flying long-haul, get measured rather than guessing a size off a chart.

The oestrogen line is the one that put me in these socks. It is also the one people are least likely to know about, because a contraceptive is not something you think of as a travel risk factor.

How risky is a long flight, really?

The risk of a clot on a long flight is low in absolute terms and roughly doubled in relative terms, and quoting only one of those numbers misleads people. TravelHealthPro puts the absolute risk for a healthy person on a flight of more than four hours at about 1 in 6,000, and notes the risk of a pulmonary embolism is much lower again.

The relative figure comes from the World Health Organization’s WRIGHT project, which found the risk of venous thromboembolism approximately doubles after a flight of more than four hours. The same applies to any travel where you sit still that long, including a coach or a train, and it climbs with the length of the journey and with several flights taken close together.

Both numbers are true at once. Doubling a 1 in 6,000 risk still leaves a small number, which is why the advice for a healthy traveller is to move around rather than to buy anything, and why the socks are aimed at people who already start from a higher baseline.

When to put on compression socks for a flight

Put them on before you get to the airport, on any journey where you will be seated for more than four hours. Four hours is the threshold the NHS uses for a long journey by plane, train or car, and the one the Cochrane trials used. My own doctor’s advice was three hours, because of the pill, which is a reminder that a personal threshold can sit below the general one.

Put them on at home, not at the gate. Your legs have had least time to swell first thing, the socks are easiest to pull on then, and doing it in a departure lounge is an undignified way to start a holiday. Keep them on for the whole journey, including the connection, because the sitting still that matters includes the three hours you spend waiting in Doha.

How to choose compression socks for travel

Choose by pressure first, then height, then fit, and ignore almost everything else on the packaging. The four things that decide whether a pair is right for you are set out below.

1. Compression level in mmHg

Pick a pressure that gives 15 to 30 mmHg at the ankle, which is the range TravelHealthPro names for travellers at increased risk. MmHg stands for millimetres of mercury and is the same unit used for blood pressure. Retail compression levels are labelled in bands, listed below from lightest to strongest.

1. Light compression: 8-15 mmHg. Below the range named for travel.
2. Moderate compression: 15-20 mmHg. The usual choice for flying and the easiest to get on.
3. Firm compression: 20-30 mmHg. Still inside the range, noticeably tighter, often what a doctor suggests for swelling.
4. Surgical compression: 30-40 mmHg. Prescribed rather than chosen.
5. Maximum compression: 40-50 mmHg. Prescribed rather than chosen.

Anything a shop sells without stating an mmHg figure is not a compression sock in any useful sense. If the number is not on the listing, that is your answer.

2. Height and style

Buy knee-high socks for travel, because that is what the trials tested and what the guidance names. Below-knee graduated compression socks are the form TravelHealthPro specifies, and everything taller belongs to a medical rather than a travel purpose. The variants you will see are listed below.

• Compression socks: knee-high, covering foot, ankle and calf. The travel option.
• Compression thigh-highs: the same idea continued up the thigh, usually medical.
• Compression hosiery: tights with graduated compression built in, including maternity versions cut over a bump.
• Compression leggings: tights supporting from the ankle up, warm under clothes.
• Calf compression sleeves: calf only, leaving the foot bare, so the foot gets no compression at all.
• Ankle sleeves and open-toe socks: partial coverage, usually sold for foot pain rather than for flying.

The sleeves are the ones to think twice about. The gradient starts at the ankle, so a sock that leaves your foot out is not doing the same job as one that does not.

3. Size and fit

Measure your calf and buy to the measurement, because fit is the only part of this you can get actively wrong. TravelHealthPro warns that poorly fitted socks can cause discomfort and, at worst, affect circulation in the leg, which is the opposite of the point. A good pair feels firm and even, not painful, and stays put without digging in anywhere.

Brands that size by calf circumference rather than by shoe size alone are the ones to look for, and their listings say so. SB SOX’s Lite knee-high in 15-20 mmHg, for example, sizes small/medium at an 11-15 in (28-38 cm) calf and large/extra-large at 14-19 in (36-48 cm), and costs $16.95 (about €15, £13). I have not worn that pair, because mine came from a Belgian pharmacy, but the published mmHg figure and the calf-based sizing are exactly the two things worth checking before you buy anything.

I have slightly bigger calves than average for my height and a standard size fits me. That is not a rule, only a reason to measure instead of assuming you need a wide fit.

4. Material

Choose a breathable fabric and let the rest go, unless you have a reason not to. Compression socks come in cotton blends, wool, nylon-and-spandex mixes and sheer fabrics, and the thicker and more opaque the fabric, the more compression it tends to hold. Sheer, elegant-looking pairs generally sit at the light end and lose their stretch sooner.

Technical moisture-wicking fabric is not necessary for a flight. Breathability is, especially if your feet get warm easily, because you will be in these for ten hours.

How to put compression socks on properly

Pull them up to where they are designed to sit and leave them alone. Compression socks should lie flat against the skin along their whole length, with the top band resting where the sock ends rather than where you would like it to end.

Three things ruin a pair, and all three are avoidable. Do not pull knee-highs up over the knee. Do not roll the top down. Do not fold it over. Each of those doubles the fabric in one spot and creates a tight band exactly where you do not want one.

What else to do on a long flight

Move your legs, drink water and skip the alcohol, because that is the advice the NHS gives every traveller on a journey of four hours or more, socks or no socks. Its list for a long journey is short: wear loose clothing, drink plenty of water, avoid alcohol, and walk around when you can. TravelHealthPro adds two practical ones, which are to keep hand luggage out from under the seat in front so you can move your legs, and to avoid anything constrictive around the waist or lower body.

Bringing your own bottle makes the water part easier, because the alternative is waiting for a trolley and a cup the size of a shot glass. A 32 oz refillable sports bottle holds close to a litre, goes through security empty and costs $24.95 (about €21, £18). Fill it after the security queue and you have a long-haul flight’s worth of water within reach.

Tight, non-stretch trousers work against you in a way compression socks do not, because they squeeze in one band rather than in a gradient. That is the reasoning behind the NHS’s loose-clothing line, and there are plenty of comfortable, loose-fitting trousers that still look like clothes rather than pyjamas.

Take your shoes off if you reasonably can, or at least loosen the laces. Feet swell on a long flight, and a shoe that fitted at check-in can be unpleasant by hour eight. Wearing something you can slip off easily solves the problem before it starts.

Travel insurance is worth a thought on the same list, for the unglamorous reason that a clot treated abroad is an expensive clot. SafetyWing’s Nomad Insurance covers travellers who are already outside their home country, which most policies sold at home will not do.

Exercises you can do in your seat

Seated exercises keep blood moving in your calves without you having to stand up, and ankle movement is the one every guideline names. TravelHealthPro’s specific instruction is to flex and extend your ankles regularly to encourage blood flow out of the lower legs. Four seated movements are listed below.

1. Ankle circles. Lift your feet clear of the floor, point your toes and circle them from the ankle, clockwise and then anticlockwise.
2. Toe-and-heel lifts. Feet flat and slightly apart, lift your toes with your heels down, then reverse it. Repeat several times.
3. Knee lifts. Sit up straight and lift one knee at a time using your leg muscles, alternating sides.
4. Knee-to-chest. Lace your fingers under one knee, lean forward slightly, draw the knee up towards your chest, hold for about 15 seconds and lower it slowly. Swap legs.

Exercises to do standing up

Standing exercises get you out of the seat, which is the part the NHS advice is really about. Walking the aisle when the seatbelt sign is off is the whole recommendation, and the two movements below are what to do while you are up there.

1. Walk the aisle. Go as far as the galley and back whenever the sign is off and the trolleys are away.
2. Calf raises. Stand straight, hold a seat back if you need to, rise onto your toes, lower, repeat.

Nobody is watching, and if they are, they are on the same flight as you and will never see you again. Someone else standing up is usually all it takes for half a cabin to decide they can too.

Who else wears compression socks

People who stand still for a living wear them as much as travellers do, for the same reason: gravity and immobility. The groups that commonly wear compression socks are listed below.

• Occupational: nurses, hairdressers, retail and hospitality staff, and anyone else on their feet for a full shift.
• Medical: people with varicose veins, leg ulcers, diabetes, recent surgery, or a condition that keeps them in bed.
• Pregnancy: including maternity hosiery cut to fit over a bump.
• Sport: runners, hikers and walkers, where swelling and aching are the complaint rather than clots.

When to stop reading and call a doctor

Call for help rather than looking anything else up if you have symptoms of a clot, and the NHS is unambiguous about which ones. It lists throbbing pain in one leg, usually in the calf or thigh, swelling in one leg, skin around the painful area that looks red, blue or darker than usual, and swollen veins. In the UK the advice is an urgent GP appointment or NHS 111.

If any of that comes with breathlessness or chest pain, the NHS says call 999 or go to A&E, because a clot that has reached the lungs is a pulmonary embolism and needs treating immediately. Outside the UK, use the equivalent emergency number. Nothing on this page is a substitute for that, and no sock is either.

WonderfulWanderings Pro Tips

The 4 tips below come from wearing compression socks on long flights since my gynaecologist told me to, and from the current NHS and TravelHealthPro advice.

1. Check whether your contraception is on the risk list before your next long-haul. The combined pill and other oestrogen-containing contraceptives are on the NHS’s list of things that make a clot more likely, and taking the pill back to back to skip periods is how I ended up in compression socks in the first place. It took a gynaecologist raising it for me to find out.
2. Put them on at home, not at the gate. Your legs are least swollen first thing, which is when the socks go on most easily, and pulling on a tight knee-high in a departure lounge is a miserable way to begin a trip.
3. Buy to a calf measurement and never fold the top down. TravelHealthPro warns that a badly fitted sock can affect circulation in the leg, and rolling or folding the cuff creates exactly the tight band the graduated design is meant to avoid.
4. Wear them for the connection too, not just the long leg. The four-hour threshold is about sitting still, and three hours in a transit lounge counts towards it as much as three hours in seat 34K does.

About the author. This guide is written and maintained by the Wonderful Wanderings editorial team. Wonderful Wanderings was founded in 2012 by Sofie Couwenbergh, and the first-hand notes here come from her own long-haul flying and from the advice her gynaecologist gave her about flying while taking the combined pill. The team covers long-haul flying, travel health and packing gear for independent travellers, including the kit that actually earns its place on a long flight, and updates this page when the published guidance changes.