Duty-free and STEB bags
Duty-free liquids purchased at airports are placed in Security Tamper-Evident Bags (STEBs). The system was designed to let passengers carry liquids over 100 ml through connecting airports without confiscation. It works reliably in some situations and fails in others that are not always obvious at the point of purchase.
What is a STEB
A Security Tamper-Evident Bag is a sealed, clear plastic bag issued by airport duty-free retailers when you purchase liquids, aerosols, or gels (LAGs) above the standard 100 ml cabin limit. The bag is designed to show visible signs of tampering if opened or interfered with after sealing.
STEBs were introduced following a 2006 security protocol developed by the International Civil Aviation Organization (ICAO). The system allows duty-free purchasers to prove that their liquid items were purchased in a secure airside environment and have not been tampered with since — theoretically demonstrating that they do not pose a security risk requiring re-screening at a connecting airport.
- The sealed bag must show no sign of tampering
- A printed receipt must be visible inside or attached showing the purchase was made at the issuing airport
- The receipt must show the date and time of purchase, matching the flight itinerary
- The bag must be intact — any cut, split, or re-seal attempt invalidates it
When STEBs work
The STEB system functions as intended in the following situations:
On a direct flight with no connection, you pass through security only at your departure airport. Duty-free liquids remain in the cabin with you for the full journey. There is no re-screening and the STEB is not challenged.
Connections within the same country where both airports operate under the same security authority typically recognise STEBs from earlier in the same journey. EU-to-EU connections are the most common example, though individual airport procedures can vary.
Many major hub airports — including most European and Middle Eastern hubs — accept valid STEBs at security re-screening points. Officers inspect the bag for tampering evidence and review the receipt rather than measuring liquid volumes.
When STEBs fail
The United States Transportation Security Administration (TSA) has not adopted the STEB recognition system at all airports or all checkpoints. When arriving on an international flight at a US airport and connecting to a domestic or onward international flight, passengers must collect their checked baggage and re-check it through customs (unless using an international-to-international connection at a limited number of airport terminals). At the subsequent domestic security checkpoint, TSA applies standard 100 ml rules regardless of STEB status. Duty-free liquids over 100 ml may be confiscated.
Any transit that requires you to leave the secure airside zone — to clear customs, collect baggage, or re-check in — breaks the STEB chain. When you re-enter security, you are treated as a new passenger and STEB acceptance is no longer relevant. Overnight connections at airports with no sterile transit facilities force this route.
Some Asian airports and certain secondary hubs do not accept STEBs at security re-screening. Officers apply the 100 ml rule regardless of bag condition or receipt. This is difficult to determine in advance — airport security procedures are not always published and can change without notice.
If you buy duty-free in Country A, transit through Country B, and then connect onward, Country B applies its own security rules. A STEB accepted at Country A's hub may not be accepted at Country B's checkpoint. The strictest-country principle applies: you are subject to the rules of whatever checkpoint you pass through.
Common pitfalls
Opening the bag
Opening a STEB for any reason — to retrieve a bottle, to show the contents to a companion, or out of curiosity — permanently invalidates it. There is no way to re-seal a STEB once it has been opened. If you need access to the contents during a layover, you lose the STEB protection for the onward connection.
Buying duty-free at a transit stop
Purchasing duty-free liquids at a transit airport — not your final departure point — creates risk at any subsequent connection. The receipt will show a transit airport purchase, and if the next connection point does not accept STEBs, or applies a stricter rule, the items will be confiscated regardless of the bag's condition.
Receipt mismatch
If the date or time on the receipt does not correspond plausibly to your flight itinerary — for example, a receipt timestamped after your onward flight departed — an officer may refuse the bag. Keep your boarding pass available alongside the STEB.
Practical guidance
Buy duty-free liquids at your final departure airport — the last security point before your destination — not at transit stops. This eliminates re-screening risk entirely, because the items stay with you in the cabin from purchase to arrival without crossing another checkpoint.
If you have a connection with known re-screening (US domestic connection, landside transfer), place duty-free liquids in your checked baggage before boarding. Most duty-free retailers will assist with checked-bag packaging on request.
For itineraries with multiple connections across different security jurisdictions, assume STEB protection may not hold at every point. Either purchase non-liquid duty-free goods, or purchase liquids at the final departure airport only.