Playing sports. Sizzling in a sauna. Even tightening one’s bra straps a tad.  

These—and many other—activities are often considered off-limits to women who’ve had lymph nodes removed in an axillary lymph node dissection (ALND), a surgery that removes lymph nodes from the armpit that is performed as part of breast cancer treatment.  

They have been branded risk factors for what is undoubtedly one of the most unpleasant side effects of treatment: lymphedema, limb swelling that occurs in as many as one in five people who have undergone an ALND. Though the condition ranges in severity, from merely unsightly to life-threatening, it typically has a significant negative impact on one’s quality of life. It’s not uncommon for those with lymphedema to experience depression, body dysmorphia, sexual dysfunction and social anxiety in the days, months and even years after their diagnosis. 

But in reality, experts say, sitting out a game of basketball, forgoing a spa day and walking around with loose bra straps are unlikely to reduce one’s risk of lymphedema. Much of the advice people who have undergone an ALND are given, it turns out, isn’t based on good science; some even runs counter to what oncologists now know are the best ways to prevent lymphedema.

Not only are many of these so-called preventive measures ineffective, but they can also “cause anxiety, and in other situations, keep people from doing the things they like,” says Babak Mehrara, MD, a plastic surgeon at Memorial Sloan-Kettering Cancer Center in New York City. He specializes in breast reconstruction and runs a National Institutes of Health–funded laboratory that was founded to research lymphedema.

In a 2015 video produced by the Lymphedema Education and Research Network, Preventing Lymphedema: Separating Fact From Fiction,” Mehrara plays myth buster, systematically evaluating the clinical value of several such preventive measures. When Cancer Health caught up with him earlier this month, he confirmed that evidence collected in the interim has continued to support the conclusions he came to in those roughly 20 minutes of screen time. Here are six of the most commonly recommended precautions—and the real story behind them.  

Engage in frequent limb elevation—propping up the legs and lifting up the arms.

Fact or fiction? “This is something that’s told to people with lymphedema and people who have had an ALND all the time,” says Mehrara, “but there is very little evidence for or against it.” His verdict: “Probably fiction.”

Avoid limb constriction—sitting in certain positions, carrying handbags in the crook of the arm and wearing skintight clothing like body-con dresses and accessories like cuff bracelets.

Fact or fiction? A study that included 15 people who had undergone both an ALND and compression tourniquet–assisted hand surgery recorded no new cases of lymphedema among them more than a year post-op. Mehrara adds a caveat:I think that [wearing] a very constricting band is probably not great for the circulation of the arm, so that should be avoided.” Wearing regular clothing that is a little tight-fitting isn’t likely to be a problem, however.

Avoid air travel.

Fact or fiction? People at risk of lymphedema often avoid traveling by plane altogether, for fear that the change in barometric pressure will overwhelm their lymphatic system. But scientific support for the likelihood of that scenario is lacking. In fact, one study involving women who had had lymph nodes removed in the course of breast cancer treatment who traveled by plane from Canada to Australia found no change in baseline impedance—the amount of time it takes electricity to travel from one leg or one arm to the other, which is a good measure of the amount of fluid in the tissues—in 95% of them. “So the verdict on this is that it’s probably fiction,” says Mehrara. However, he would like to see more studies on the relationship between air travel and lymphedema risk conducted in the future.

Avoid extreme temperatures.

Fact or fiction? Contrary to what people who have undergone an ALND are commonly told, heat therapy may actually reduce the symptoms of lymphedema. One prospective study found that of 98 people with lymphedema who underwent a round [of heat therapy], 85 saw a decrease in the volume of their affected limb(s), three quarters by more than 50%. “I think people have to be careful about this because many patients who have had surgery experience changes in the sensitivity of their skin, so extreme heat is probably not a good thing [because] it’s possible for them to get a burn,” said Mehrara. “But some heat—for example, in a hot tub—is probably OK.” 

Avoid physical exercise.

Fact or fiction? Mehrara minces no words here. “Exercise in particular has been shown by several studies to help patients with lymphedema, particularly when combined with weight loss,” he says. “So telling people to avoid exercise is definitely the wrong advice based on the wealth of scientific literature.” In particular, Mehrara recommends aerobic activities like running, swimming and walking, ideally under the supervision of a physical therapist. (In recent years, many breast cancer survivors have taken up dragon-boat racing, which originated in China about 2,500 years ago. You can read more about that here.)

Avoid weight gain.

Fact or fiction? “Increasing weight and obesity cause inflammation, [which] has been shown to cause lymphatic abnormalities in both patients and in animal models,” Mehrara explains. “As a result, obese patients have a decreased ability to transport lymph. The combination of this baseline decrease in lymphatic function and surgery (and radiation) increases the risk of developing lymphedema by at least twofold.” He points to the results of several recent animal studies, including 2016’s “Exercise training improves obesity-related lymphatic dysfunction,” which concluded that damage to the lymphatic system incurred by obesity is reversible with diet-induced weight loss and regular exercise.

The bottom line? “The best preventive measures that are proven to work are weight loss and exercise,” Mehrara tells Cancer Health. “Anti-inflammatory diets, like the Mediterranean diet, by inference, are also likely to be effective.” In short: Stay active, and pile your plate with fish fillets and fresh vegetables!

To learn more about treatment for breast cancer and its side effects, click here.