Transit airports: customs rules when you're not staying

title: "Transit airports: customs rules when you're not staying" description: "What 'in transit' actually means at customs, the difference between sterile and non-sterile transit, what triggers a re-inspection, and the items that get confiscated even though you're just changing planes." category: "traveling" estimatedReadMinutes: 6 lastUpdated: "2026-05-16"

Transit looks like it should be a non-event for customs — you don't leave the airport and your goods don't enter the country. In practice, several layers of rules apply, and some of them can confiscate goods even though you're "just connecting".

Two kinds of transit

Sterile transit — you stay airside, you don't pass through immigration, and your bags continue through-checked. This is the cleanest scenario.
Non-sterile transit — you collect your bags, pass through immigration or claim them landside, and re-check for the onward flight. This is treated as entry and exit.

Whether you are in sterile transit depends on the airport's facilities, the carrier (some require you to collect bags), and your visa / nationality (some passports require entry even for transit).

What still applies in sterile transit

Even when sterile, the aviation security rules of the transit airport apply to your carry-on:

Liquid rules — most jurisdictions cap carry-on liquids at 100 ml per container, in a single 1-litre clear bag. Duty-free liquids bought at the origin airport can be confiscated at a transit security re-screening if they aren't in a sealed STEB (Security Tamper-Evident Bag) plus proof of purchase.
Lithium batteries — power banks and spare lithium batteries cannot go in checked baggage. Transit airports re-enforce this if you re-check.
Sharp objects and tools — some transit airports are stricter than the origin airport. A nail file accepted at origin may be confiscated at a re-screen.
Powders — Australia, the US (on US-bound flights), and some others have restrictions on powders in carry-on.

The classic example: a litre of whisky bought at duty-free in Singapore, transiting through Heathrow on the way to New York, can be confiscated at the Heathrow security re-screen if it isn't STEB-sealed.

What applies in non-sterile transit

You are entering the transit country, even briefly. That means:

The transit country's immigration rules — some passports need a transit visa.
The transit country's customs rules — but only for the goods you bring landside. Through-checked baggage stays in customs control.
Re-export within the transit window — some jurisdictions require you to leave within 24–72 hours.

If your visa for the destination is denied or you miss the onward flight, you may need to formally clear customs and stay in the transit country until rebooked.

Items that get caught in transit even when sterile

Liquid duty-free without a STEB — most common confiscation.
Power banks above watt-hour limits — re-screened against the strictest of the route's airlines.
Cannabis-derived products — even where legal at origin and destination, if the transit country prohibits them, they are illegal during transit. Don't transit through cannabis-prohibitive jurisdictions with CBD.
Vapes — similar to cannabis: legal at origin, legal at destination, can still trigger confiscation in a transit country that bans them.
Cash above the transit country's threshold — some jurisdictions count transit travellers in their cash-declaration regime.

Practical checklist

Before booking transit through a third country, check:

Does my passport allow airside transit, or does the transit country require a visa?
Are any of my carried goods prohibited in the transit country (vapes, CBD, knives, certain electronics)?
If I'm carrying duty-free liquids, are they in STEB? Is my route + airline compatible with the most restrictive jurisdiction's liquid rules?
Am I re-checking bags? If so, do I need to claim them and clear customs?
Is my total transit time within the transit country's airside dwell limit?

Forced overnight transit

If your onward flight is cancelled and you must stay overnight, most airports have a transit hotel airside. Otherwise, you formally enter the transit country (immigration + customs apply) and recover the bags as a normal arrival.

Useful linked pages

Country profile pages list each transit hub's quirks where known.
The lithium battery shipping guide covers air-cargo and carry-on lithium rules.
For duty-free, the duty-free allowances guide explains the rule of "allowance applies to arrival, not departure".

Not legal advice. Verify against each transit country's customs and aviation authority.