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 journal Archives of Disease in Childhood.

In a new systematic review of all the evidence relating to flying with allergies, the research team found that allergic reactions to foods are in fact 10 to 100 times less common during flights than they are ‘on the ground’ – although they note that 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, who led the study, 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 aerosolised food particles, even if they are allergic to very small amounts.”

However, the authors did find evidence that there is risk from passengers touching contaminated surfaces on the aircraft, and then transferring allergens to their mouths. This probably explains why some people think they do react to airborne allergens. They recommend a simple solution.

Dr 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, tabletops, and seat-back entertainment screens. If food-allergic people have time to clean their seat area with something like a baby wipe or antibacterial wipe, they are much less likely to have these type of 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 concerns about the issue from passengers.  The published study is a summary of the full report and its findings are also referenced on the CAA’s passenger health information.

 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 deshelling 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. 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.

Since cleaning surfaces is important, allowing food-allergic passengers to board the plane in advance can 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.

The researchers say that public 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. But they do recommend that passengers at risk of food anaphylaxis should carry adrenaline [epinephrine] auto-injectors, such as an EpiPen, in their hand luggage.

Dr 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.”

Simon Williams, Chief Executive of Anaphylaxis UK, also 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."