In carry-on bags, powder-based substances exceeding 12 ounces (350 millilitres) are subject to additional screening at U.S. security checkpoints. These substances must be placed in a separate bin for X-ray screening. If security personnel cannot resolve any issues with the powder during this screening process, the substance will not be allowed on the aircraft and will be disposed of. Pack powders over the specified limit in your checked baggage whenever possible to avoid delays and complications.