The US Transportation Security Administration (TSA) introduced the new powder rule on 30 June 2018.
The new rule means that powdered substances with a volume of more than 350ml in hand luggage will be subjected to more thorough screening on all flights to the USA. If inspectors cannot clearly establish what the powder is, it will be confiscated. US carriers such as American Airlines are therefore advising passengers to pack cosmetics, spices, protein powder and other powder-like substances of over 350ml in their checked luggage and not in their carry-on bags.
This advice does not apply to flights departing from the USA or US territories, as the TSA has already introduced improved processes at its security checkpoints.