Some items should not be carried on an aircraft in either carry-on or checked luggage because of the danger they represent for the passengers and crew. Many of these items are commonly used at work or in the home, but may become a hazard in flight due to changes in temperature and pressure that can cause items to leak, generate toxic fumes or start a fire. Some exemptions are allowed for medical devices and personal care items. If in doubt, check with your air carrier.

In the wake of the events of 11 September 2001, the FAA has prohibited the following items from airplane cabins (though they can be carried as checked luggage):

• Knives of any length, composition or description
• Cutting instruments of any kind and composition, including carpet knives and box cutters (and spare blades), any device with a folding or retractable blade, ice picks, straight razors, metal scissors and metal nail files
• Corkscrews
• Baseball/softball bats
• Golf clubs
• Pool cues
• Ski poles
• Hockey sticks
• When in doubt, transport item in checked baggage

Explosives and Firearms: Matches, sparklers, other fireworks, flares, gunpowder, ammunition or other ordnance, blasting caps, dynamite, loaded firearms (in some cases, unloaded firearms and sporting ammunition may be carried in checked baggage if properly packed)
Note: In the United States, federal laws apply to aircraft and to the secure areas of the airport such as the gate areas. State or local laws concerning the carrying of concealed or unconcealed weapons do not apply. Attempting to enter these areas with weapons may lead to your arrest.

Other Weapons: Knives of any kind, throwing stars, swords, or other items commonly used in martial arts competitions. Rules in other countries will vary with respect to the carraige of knives and other weapons.

Gases and Pressure Containers: Flammable aerosols like hair spray, spray paint, or insect repellant; carbon dioxide cartridges, oxygen tanks (scuba or medical), mace, tear gas, pepper spray, self-inflating rafts, and deeply refrigerated gases such as liquid nitrogen

Flammable Liquids and Solids: Gasoline, propane, butane, and other fuels; lights with flammable reservoirs, matches, flammable paints, paint thinners, some cleaning solvents, some adhesives, cigarette lighters, and lighter fluid. Personal care items containing flammable perfume, aerosols, or other hazardous material may be carried on board if each container is less than 16 fluid ounces (473 ml) and the total is less than 70 fluid ounces (2.07 liters).

Oxidizers and Organic Peroxides: Bleach, nitric acid, fertilizers, swimming pool or spa chemicals, and fiberglass repair kits

Poisons: Weed killers, pesticides, insecticides, rodent poisons, arsenic, and cyanides

Infectious Materials: Medical laboratory specimens, viral organisms, and bacterial cultures

Corrosives: Drain cleaners, car batteries, wet cell batteries, acids, alkalis, lye, and mercury

Organics: Fiberglass resins, peroxides

Radioactive Materials: Smoke detectors, radioactive pharmaceuticals, and other radioactive materials

Dry Ice (frozen carbon dioxide): Up to four pounds (8.8 kg) may be carried on board for packing perishables providing the package is vented

Magnetic Materials: Strong magnets such as those in some loudspeakers and laboratory equipment

Other items: Wet-cell batteries, chemical oxygen generators (either used or unused), or any equipment containing fuel or other flammable liquids

Declaring Hazardous Materials: In the U.S., you must declare hazardous materials to airlines, express package carriers, or the U.S. Postal Service. Violations carry a civil penalty of up to $27,500 for each occurrence and, in appropriate cases, a criminal penalty of up to $500,000 and/or up to five years imprisonment.