When airline employees or passengers ignore protocol around peanuts, the results can turn tragic. Here’s what you need to know about bringing peanuts and peanut butter on the plane.

Last year, four-year-old Fae Platten was flying home to England from a family vacation in Spain. Before boarding, her parents told Ryanair’s crew about their daughter’s severe peanut allergy. Flight attendants made three announcements asking passengers not to eat peanuts. Despite that, a man four rows behind Fae decided to eat the snack he’d brought onboard: a bag of mixed nuts, including peanuts. Fae’s face swelled and her lips blistered. Her mother raced her to the front of the cabin, away from the peanut dust. Nevertheless, Fae went into anaphylactic shock, stopped breathing, and went unconscious. Luckily, a paramedic was on board to inject her with an EpiPen. When the plane landed, an ambulance took her to a hospital, where she recovered.

This and other horror stories, like that of 13-year-old Natalie Giorgi, whose last words while dying of a peanut-induced allergic reaction were, “I’m sorry, mom,” should make those of us who take public transportation consider whether it’s acceptable to bring peanuts along for the ride.

When allergic people are exposed to peanuts, “an immunologic explosion occurs,” says Samuel Friedlander, an allergist at University Hospitals Case Medical Center in Cleveland, Ohio. “People can have closing of the throat, coughing, trouble breathing, hives, and swelling. In the worst case, low blood pressure and death can occur with anaphylaxis.”

It’s rare for peanut-allergic people to react severely from air on a plane—it’s more common for the smell to make them uncomfortable—but as evidenced by little Fae’s case, it does happen. “On planes the air is recirculated,” explains Allie Bahn, a food-allergy advocate, “and peanut dust can spread easily.”

According to an NIH study, at least 1 in 100 Americans is allergic to peanuts (which are actually not nuts but legumes). And according to the American Academy of Allergy, Asthma & Immunology, peanuts represent children’s most common food allergy (milk comes in second, shellfish third).

“In children, the incidence continues to rise,” notes Devang Doshi, who heads the allergy and immunology department at Michigan’s Beaumont Children’s Hospital.

“Your life changes in every way when you or a loved one is diagnosed with a food allergy,” says Jennifer Kurko, whose two daughters’ food allergies inspired her to start Kiss Freely, an allergy-friendly line of beauty products. “Simple tasks become fraught with danger. We’ve made many accommodations for the safety of others, including no smoking during flights and the banning of all sorts of objects. Banning peanuts helps to keep a small but rapidly growing population safe.”

“Most people would never intentionally expose another person to an allergen that could harm them,” says Diane Gottsman, an etiquette expert whose child has severe allergies. “It’s a courtesy to be cognizant of others in dire situations, which definitely includes allergies to specific foods, pets, and smoke.”

Anne Klaeysen, who leads the New York Society for Ethical Culture, adds, “Given that peanut allergy is the most common cause of food-related death, following the practice of ‘When in doubt, do no harm’ in these situations would be ethical.”

Not everyone agrees that peanuts should be banned: Paul Ehrlich, a pediatric allergist at NYU Langone Medical Center, thinks it’s all right to bring peanuts onboard if you’re careful about it. “I’m not going to say that having peanuts on a plane is never a threat,” he says. “However, if the person with peanuts doesn’t touch the allergic person or spread peanut butter on the allergic person’s seat or immediate environment, then it’s okay.”

Billie Frank, who owns the trip-planning company Santa Fe Traveler, was on a US Airways flight when, during takeoff, the crew announced that, due to a passenger’s allergy, no one could eat any kind of nut. “They were going to serve peanuts but reverted to pretzels,” Frank recalls. “I’m allergic to wheat and had brought almonds to snack on. I was unable to eat on the flight. I thought it unfair that a whole plane was held hostage to one person’s allergy. I’m sensitive to perfume and allergic to cats and some dogs, yet I have to ride in the cabin with them.”

As of now, there are no laws against bringing peanut products onto public or private property, though some schools ban peanuts and many establish “peanut-free zones.”

Most airlines’ peanut policies seem phrased to protect them from getting sued (as United was in 2013 when its employees failed to make the announcement they had promised to a woman with a severe peanut allergy). Most policies go something like this, from American Airlines: “We cannot guarantee customers will not be exposed to peanuts during flight, and we strongly encourage customers to take all necessary medical precautions to prepare for the possibility of exposure.”

In 2018 Southwest announced that it would stop serving peanuts in flight “to ensure the best onboard experience for everyone, especially for customers with peanut-related allergies.”

Some carriers, like JetBlue, accommodate allergic passengers by creating “nut buffer zones” around the affected person.

Within the allergic community, Delta is known as being the most accommodating airline. “We choose Delta because other people with food allergies recommend them,” Kurko says. “They flag your reservation and make an announcement onboard that there’s a traveler with a nut allergy and that they won’t be serving nuts. They also request that other passengers refrain from eating nuts. It isn’t foolproof—the flight attendants can be inconsistent in making the announcement—so we carry enough epinephrine to get us to our destination should the need arise.”

Delta also allows people with allergies to pre-board in order to wipe down their seating area. “Unfortunately, we still can’t guarantee that the flight will be completely peanut-free,” says Michael Thomas, a Delta spokesperson. “Flight attendants are of course trained on how to deal with in-flight medical situations.”

If you’re planning to bring peanut products on a flight, you should know a few things. First: The TSA will confiscate any jar of peanut butter containing more than 3.4 ounces, since it’s considered a gel. If you need to travel with peanut butter, put it in your checked suitcase or stow a tiny pouch of it in your carry-on.

Second, if you’re eating any food that could threaten others, clean up anything you spill. “That way, a child with an allergy won’t accidentally touch or ingest the allergy food,” Friedlander says.

Tara Zamani, a nutritionist, adds, “Keep peanut butter in a closed container. If you want to use it as a spread, prepare your sandwich prior to coming on to the plane, wrap it in foil, and put it in a Ziploc. It’s best to ask your neighbors if they have allergies. If so, change seats if you plan on consuming what they’re allergic to.”

To be an even more considerate co-traveler, heed Doshi’s advice: “With the continued growing incidence of food allergies, the safest thing to do is avoid carrying foods which may place other passengers’ health and safety at risk.” From his medical perspective, it’s dangerous for airlines to be as lax as they are about having peanuts on their aircrafts. “Emergency medications may not be readily available. This would place someone experiencing an allergic reaction at high risk for morbidity and or mortality.”

If you or your child has a peanut allergy, know what you can do to keep safe and comfortable during a flight. Bahn says, “I always makes sure to have the following with me: disinfecting wipes for wiping down the seat and tray table as soon as I board, plenty of epinephrine, an antihistamine like Benadryl, and my own safe snacks.”

Kurko adds, “We do not allow our girls to use the pillows or blankets, as they are usually not cleaned between flights.”

Doshi tells his patients that their epinephrine pens and other remedies should display a prescription label bearing the passenger’s name to sidestep any trouble with the TSA. He also recommends packing a doctor’s note listing all allergies and medications.

Other sound advice includes checking the flight menu before booking and calling to notify the airline about your allergy as soon as you’ve made your reservation. Tell the gate agent about it as soon as you reach your gate. And tell the flight attendants about it as soon as you board. Ask them to make announcements, and to keep nut-containing snacks and meals far from you. Once you’re settled on the plane, politely tell those seated near you about your allergy.

“If someone pulls out a bag of nuts,” Gottsman says, “let that passenger know that you or your child is severely allergic and ask if they would mind holding off until you talk to the flight attendant about arranging a seat change.”

Lianne Mandelbaum encourages people to push the airlines to change their inconsistent policies regarding food allergies. Her site, No Nut Traveler, offers links for signing a petition, filing a complaint, and contacting lawmakers. Mandelbaum became an activist after a United manager at Denver’s airport refused to make an announcement about her child’s peanut allergy. The employee told her, in front of her eight-year-old son, “If you think he’s going to die, don’t get on the plane.”

They didn’t get on the plane.

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Avital Andrews also covers travel for the Los Angeles Times, Sierra, Outside, and the Huffington Post. Follow her on Twitter @avitalb.

(Photo: Thinkstock/Shutterstock.)