Surface residues pose the main risk, possibly heightened by fast turnarounds
There is no evidence for the commonly held belief that nut allergens can be spread through aircraft ventilation systems, say allergy and aviation medicine specialists in an evidence review published in the Archives of Disease in Childhood.
Allergic reactions to foods are in fact 10 to 100 times less common during flights than they are 'on the ground,' they say, although this could be due to passengers with food allergies taking more precautions when flying.
Instead, allergen residues on surfaces, such as tray tables, and seat-back video screens, were found to pose the main risk.
Paul Turner, Clinical Professor in Anaphylaxis and Allergy at Imperial College London, said: "The message is that people shouldn't be worried about what food is being transmitted in the air when they fly. We didn't find any evidence that nut particles could travel through the cabin ventilation system on airplanes and cause reactions. On top of that, the vast majority of people with food allergies don't react to the smell of food, even if they are allergic to very small amounts."
However, the authors did find evidence that most of the risk is actually from passengers touching surfaces on the aircraft and then transferring allergens to their mouths. They recommend a simple solution.
Professor Turner explained: "The one thing people must do to protect themselves is to clean their seat area. Allergenic food is really sticky, and can be found on seat surfaces, table tops, and seat-back entertainment screens. If food-allergic people can board first, and have time to clean their seat area with something like a baby wipe or antibacterial wipe, they are much less likely to have accidental reactions."
The UK's Civil Aviation Authority (CAA) commissioned the authors to investigate and report on the risks of flying with allergies, in a response to some of the misconceptions.
Around 2–3% of children and 1–2% of adults in the UK have a food allergy, with similar rates observed in medium to high income countries. Food allergy is the most common cause of anaphylaxis, a potentially life-threatening allergic reaction.
The researchers undertook a systematic review of all the published evidence dating back to 1980. They found that, with the notable exceptions of vapours from fish/seafood and exposure to occupational wheat flour, allergic reactions to aerosolised foods are rare.
While peanut allergens can be detected at very low levels in the air when shelling nuts, the dust settles quickly and can only be detected in very close proximity to the nuts, implying that very little dust circulates in the air.
What's more, aircraft cabin ventilation systems are designed to circulate air across the aircraft, rather than along the cabin, so minimising the potential for spreading passenger-generated contaminants through the cabin.
Air is completely exchanged every 3–4 minutes during a flight. This compares with every 10 minutes for hospitals and classrooms. In modern large commercial aircraft, around half of the air intake is recirculated air that has passed through particulate air filters which effectively remove dust, vapours, microbes, and capture aerosolised food particles at the same time. The other half comes from outside.
Simon Williams, Chief Executive of Anaphylaxis UK, commented on the findings, saying: "A key take-home message is the importance of passengers cleaning their seat area, including the tray table and the seat-back entertainment system."
Allowing food-allergic passengers to pre-board may be helpful in this respect, say the authors, who note that the US Department of Transportation already requires airlines to allow passengers with nut allergies to do this.
While announcements requesting passengers not to consume nuts during the flight are unlikely to reduce the risk of in-flight reactions, and might provide false reassurance, they do recommend that passengers at risk of food anaphylaxis should carry adrenaline [epinephrine] auto-injectors, such as an EpiPen, in their hand luggage.
Professor Turner says the next stage is to inform and influence airline policy. He explains: "We're having discussions with a number of major airlines as well as patient groups and anaphylaxis charities, to see if we can get some consistent changes in airline policy across airlines operating out of the UK and internationally. That will help to reflect what the evidence is and really make a difference to food-allergic passengers."
Review: Flying with nut and other food allergies: unravelling fact from fiction Doi 10.1136/archdischild-2024-327848 is published in Archives of Disease in Childhood
External funding: UK Medical Research Council; UK Civil Aviation Authority
