There are two very different types of spraying that happen on commercial aircraft before takeoff, and which one you’re thinking of depends on what you saw. The bright orange or green fluid sprayed on the outside of a plane is de-icing fluid, a glycol-based solution that prevents ice from forming on the wings. The mist you might see sprayed inside the cabin is either an insecticide (required on certain international routes) or, more recently, a disinfectant. Each serves a completely different purpose.
De-Icing Fluid on the Wings
If you’ve watched ground crews aim high-pressure hoses at a plane’s wings and fuselage during winter, that’s de-icing. The fluid is a mixture of propylene glycol (or sometimes ethylene glycol) and water, essentially a concentrated antifreeze. It’s applied hot, and the combination of heat and hydraulic force strips frozen contaminants off the aircraft’s critical surfaces. Even a thin layer of ice on a wing can disrupt airflow enough to be dangerous, so regulations require the plane to be clean before it rolls toward the runway.
There are four types of de-icing and anti-icing fluids, each with a different job:
- Type I is the most common de-icing fluid. It has a high glycol content and low viscosity, and it’s always applied heated and diluted. It does a great job removing existing ice but offers limited protection against refreezing if snow or freezing rain continues to fall.
- Type II contains thickening agents that let it cling to the aircraft’s surface during taxi and ground operations, then shear off once the plane accelerates past about 100 knots on the takeoff roll. This gives it a longer “holdover time,” the window during which the plane stays protected.
- Type III is a middle ground, thicker than Type I but much thinner than Type II. It’s designed for slower aircraft that don’t reach the high rotation speeds needed to shed thicker fluids.
- Type IV offers the longest holdover time of any fluid and is the go-to choice when heavy snowfall or freezing precipitation is expected to continue between de-icing and takeoff.
The green, orange, or yellow color of these fluids is intentional. It helps ground crews see exactly where the fluid has been applied and confirm full coverage. A plane might get a Type I spray first to remove existing ice, followed by a Type IV application to keep ice from re-forming while it waits in the takeoff queue. The glycol/water ratio determines the freezing point: pure propylene glycol won’t freeze even in extreme cold, while ethylene glycol reaches its lowest freezing point at roughly a 70% concentration rather than at full strength.
Insecticide Spraying Inside the Cabin
The mist you sometimes see flight attendants or ground crew spraying down the aisle of an international flight is insecticide. This practice is called “disinsection,” and its purpose is to prevent disease-carrying mosquitoes and other insects from hitching a ride between countries. Diseases like malaria, dengue, and Zika can spread when infected mosquitoes are transported into regions where they don’t normally exist, so certain countries require all arriving aircraft to be treated.
The active ingredients are typically permethrin or d-phenothrin, both synthetic compounds in a class of insecticides modeled after a natural chemical found in chrysanthemum flowers. They’re effective at killing insects on contact or shortly after exposure. The WHO published its comprehensive guide to aircraft disinsection methods in 2021, updated in 2023, and individual countries set their own requirements based on that guidance.
How Disinsection Is Applied
There are three main approaches. In the “blocks-away” method, flight attendants walk through the cabin spraying an aerosol can just after the doors close and the aircraft pushes back from the gate. Passengers are on board for this. In the “top-of-descent” method, the cabin is sprayed during the final approach before landing. Both of these happen with passengers present.
The third option is the residual method: a long-lasting permethrin treatment is applied to cabin surfaces (walls, overhead bins, carpet, upholstery) while the plane is empty, and it remains effective for several weeks. Countries like Australia, New Zealand, Barbados, Fiji, Jamaica, and Chile accept this residual approach as an alternative to spraying with passengers on board.
Which Countries Require It
According to the U.S. Department of Transportation, countries that require aerosol spraying on all inbound flights with passengers present include India, Panama, Madagascar, Ecuador (Galápagos and inter-island flights), Tanzania, Uruguay, Trinidad and Tobago, Seychelles, Guyana, Grenada, Kiribati, Zimbabwe, and Timor-Leste. Australia, New Zealand, and several Caribbean and Pacific island nations require disinsection but allow the residual method instead.
If you’re flying domestically within the U.S. or between countries that don’t mandate disinsection, you won’t encounter this. It’s almost exclusively an international practice tied to specific tropical and subtropical destinations.
Disinfectant Spraying After COVID-19
During the pandemic, many airlines added a third type of cabin spraying: antimicrobial disinfectant applied between flights using electrostatic sprayers. These devices give the disinfectant an electrical charge so it wraps around surfaces and reaches areas a simple wipe-down would miss. The EPA evaluated three categories of active ingredients used in these sprayers: chlorine-based compounds, hydrogen peroxide, and quaternary ammonium (the same family of chemicals in many household disinfectants).
This type of spraying typically happens while the cabin is empty during turnaround, so passengers rarely see it. Some airlines still use electrostatic or fog-based disinfection as part of their regular cleaning routine, though the practice has scaled back from its peak in 2020 and 2021.
Is Any of This Harmful to Passengers?
De-icing fluid never enters the cabin. It’s applied entirely to the aircraft’s exterior, and any residue shears off during takeoff. Passengers have no meaningful exposure.
Cabin insecticide spraying is the one that raises the most concern. Permethrin and d-phenothrin are considered low-toxicity to humans at the concentrations used in aircraft, but some passengers report headaches, throat irritation, or breathing discomfort during aerosol applications. People with asthma or chemical sensitivities may be more affected. The WHO’s position is that the concentrations used in disinsection fall within safe exposure limits, though research into long-term effects on frequently exposed crew members is ongoing. If you know your flight will involve cabin spraying, you can cover your nose and mouth with a damp cloth during the brief application.
Disinfectant residues from electrostatic spraying are generally dry by the time passengers board, and the active ingredients break down relatively quickly on surfaces. The EPA requires that only registered products be used, applied according to label directions.