Travelers have long been warned about the risk of blood clots during flights, especially long-haul journeys. Often, this advice comes with a recommendation to wear compression socks. But are compression socks truly essential for travel, or is it just another travel myth?
“It’s absolutely okay to use them,” confirms Dr. Joshua Beckman, a vascular medicine expert at UT Southwestern Medical Center. However, he points out that scientific evidence doesn’t definitively quantify how much benefit travelers actually receive from them.
Compression socks, also known as graduated compression stockings, are designed to apply pressure at the ankles, gradually decreasing as they move up the leg. This compression aids blood circulation by encouraging blood flow from the legs back to the heart.
Deep vein thrombosis (DVT), a condition involving blood clot formation in a large vein, often in the leg, affects a significant number of people. In the U.S. alone, approximately 666,000 individuals were hospitalized with DVT in 2020, according to the American Heart Association’s latest statistics. Furthermore, 432,000 were hospitalized for pulmonary embolism (PE), where a clot travels to the lungs. Venous thromboembolism (VTE), encompassing both DVT and PE, was cited as a factor in nearly 81,000 deaths in 2021.
Symptoms of DVT can include leg pain, swelling, and skin that is warm to the touch. Pulmonary embolism symptoms may manifest as shortness of breath, coughing, and chest pain.
Extended travel, particularly long flights, increases the likelihood of VTE by 1.5 to fourfold, according to a Cochrane Database of Systematic Reviews review updated in 2021.
Despite the increased risk associated with travel, developing dangerous blood clots remains statistically rare. A 2007 research review in the Journal of Internal Medicine estimated approximately 4.8 cases of severe pulmonary embolism per million flights exceeding 12 hours. The risk of DVT within four weeks following a flight of at least four hours was estimated at 1 in 4,600 flights.
Dr. Eri Fukaya, a vascular medicine specialist at Stanford University, explains that air travel can create “a perfect storm for a clot.” However, she emphasizes that pre-existing risk factors play a more significant role.
Individuals at higher risk of VTE include older adults, smokers, those with obesity, or those with a family history of blood clots. This also includes individuals with a prior history of clots, recent cancer treatment, or those taking estrogen, Fukaya notes.
She uses an analogy of a bucket to illustrate risk. Individuals whose “bucket” is already nearly full due to these pre-existing factors are at a higher risk. In such cases, air travel might be the “overflowing” factor that triggers a blood clot.
Prolonged immobility from sitting in cramped airplane seats for extended periods contributes to the risk, she adds. Dehydration, often exacerbated during flights as passengers avoid drinking fluids to minimize bathroom trips, can also thicken the blood, further increasing risk.
However, Dr. Beckman reiterates that the risk of developing severe blood clots solely due to flying is so low that studying preventative measures becomes challenging.
He cites a 2022 study in the American Journal of Obstetrics and Gynecology: Maternal-Fetal Medicine, which examined VTE risk in a high-risk group: pregnant and postpartum women. While the study found a slightly elevated risk in women who flew compared to those who didn’t, the difference was “very tiny” – 0.07% versus 0.05%, respectively.
These minute differences highlight the difficulty in definitively proving the effectiveness of compression socks in preventing blood clots in air travelers, Beckman states. “If the baseline risk is already very low, reducing it further becomes statistically hard to measure in a study.”
The Cochrane review analyzed data from 2,918 participants across 12 randomized clinical trials. It found strong evidence that compression stockings reduce the risk of asymptomatic DVT during flights longer than four hours. However, the review couldn’t draw conclusions about the impact on death, pulmonary embolism, or symptomatic DVT due to the absence of these events in the trial participants.
The American Society of Hematology guidelines do not recommend compression socks for low-risk travelers on short flights. They suggest considering them for longer flights only for individuals at high risk of blood clots.
Hospital studies have demonstrated the effectiveness of compression socks in preventing blood clots in post-surgical patients, Beckman acknowledges. However, he notes that the benefits are less clear for non-surgical patients on bed rest. “If establishing a benefit is difficult even for sick, bedridden hospital patients, it’s even more challenging to prove benefits for healthy, mobile individuals traveling for leisure.”
Despite the limited definitive evidence for travelers, Dr. Beckman emphasizes that if a doctor recommends compression socks for any reason, “absolutely” follow that medical advice.
For travelers concerned about blood clots, his primary advice is to “get up and walk around every couple of hours. Drink plenty of water.”
Dr. Fukaya adds to this advice, suggesting seated exercises such as flexing calf muscles and rotating ankles in “big circles, both directions.” She also recommends removing shoes and wiggling toes to promote blood circulation.
And if you are already using compression socks and find them comfortable, there’s no need to discard them.
Like Dr. Beckman, Fukaya confirms they are not harmful. Unlike Beckman, she is a personal advocate and wears them regularly.
Compression therapy has historical roots dating back to ancient times, she notes. Compression socks stimulate calf muscles during movement and can help prevent swelling.
“I wear them almost daily,” Fukaya shares, explaining she started to better understand her patients’ experiences and discovered “my legs feel significantly better wearing them.”
Individuals with poor circulation due to peripheral artery disease should exercise caution with compression socks, she advises. However, for most others, experimenting to find what works best is safe.
The market offers a wide variety of compression socks, ranging from those marketed towards athletes to medical-grade options. Medical-grade socks are categorized by pressure levels measured in millimeters of mercury (mmHg), but Fukaya finds these ratings less critical. The actual pressure varies depending on leg size, and rating standardization is lacking.
Pressure rating is relative, she explains. “It’s similar to ordering food at a restaurant and choosing ‘mild, medium, or spicy’.” She recommends starting with a medium compression level and adjusting to “mild” or “spicy” based on personal comfort.
“You could even try wearing a sock on only one leg during travel to compare how each leg feels afterward,” she suggests. Fukaya prefers knee-high versions over thigh-high ones. If knee-high socks are slightly too long, avoid rolling them down, as this can create a tourniquet effect.
Compression socks are perfectly acceptable for those who find them beneficial, concludes Beckman. However, when prioritizing health for travel, he suggests focusing on other essentials like sunscreen.
“Travelers already have numerous health considerations,” he states. “It’s also important to reassure them and alleviate concerns about things that are not really necessary to worry about.”
