First they came for our shampoo, now they're coming for our talcum powder.

Travellers on international flights heading to the United States will face more screening of powdered substances in carry-on bags, starting June 30.

A Transportation Security Administration spokesman said yesterday that the change applies to passengers carrying more than 350 milliliters of powder, the AP reports. That's about the same size as a can of fizzy drink.

Those carrying larger amounts of powders – including cosmetics, ground coffee or other food items – could have their bags opened and tested for explosives.

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It's recommended that amounts over the 350 millilitre limit are stored in checked-in baggage and smaller amounts are removed from carry-on bags for a better view in the X-ray.

The policy was enacted partly in response to a foiled bomb plot on an Etihad Airways plane flying to Abu Dhabi, from Sydney last July.

The TSA said the extra screening was already in place for domestic flights in the US.

While this latest security effort isn't an outright ban, a traveller could risk having larger amounts powders discarded before boarding a plane – not an ideal situation if you're carrying powdered baby formula or have been spice shopping in Morocco.

"We encourage people to divest certain items – especially organic items – in order to get a clearer view of what's going on inside the bag," said Mike England, a TSA spokesman told USA Today. "It's something we advise people to do. We're asking our foreign partners to do what we're already doing domestically."

While the agency's main concern agency's concerns was materials that could be used to construct an explosive in flight, it also identified fentanyl and pepper powder in the cabin as a potential threat.

While the TSA publishes a list of what is permissible and banned on its website, it has yet to update its rules for powders with the new 350 mililitre limit.

This is the most recent change to airport security in the US following 9/11.

In 2006, a ban on liquids over 100ml in carry-on baggage was brought into place after a failed bomb plot.

Full body scanners were introduced in 2010, after an underwear bomber tried to detonate an explosive device on a flight from Amsterdam to Detroit.

Last year, travellers were asked to remove electronic devices larger than a cellphone for security screening. Lithium-ion batteries were also restricted in cabin baggage due to fears of battery fires.

As you'd expect, the new restrictions could cause more delays in security lanes as agents and passengers adjust to the changes.

"Whenever there are new requirements, there are slowdowns at the checkpoint during the transition period," Gary Leff, the author of the aviation blog View from the Wing, told the New York Times.

"During the week you have more regular travelers who adapt more quickly, then you tend to see slowdowns around the holidays as those who fly less frequently, going on past expectations, find out they are carrying something no longer allowed that triggers secondary inspection, and slows down the line."