The in-flight liquid limit was introduced in 2006 after British police foiled an Islamist terror plot to detonate explosives on transatlantic flights. They planned to smuggle liquid explosives disguised as soft drinks in their hand luggage, in what would have been the deadliest terror attack since 9/11.

The 100ml (3.4 oz) limit on liquids in carry-on baggage was implemented globally following a foiled 2006 terror plot in the UK, where plotters intended to use liquid explosives disguised as soft drinks to bring down multiple aircraft. Security experts determined that 100ml was a "safe" threshold: it is a volume too small to create a catastrophic explosion on its own, yet large enough to allow for essential toiletries. By requiring all liquids to be in small containers and placed in a single quart-sized clear bag, security officers can more easily scan and identify high-density liquids using X-ray technology. In 2026, however, this rule is finally beginning to disappear at major "gold standard" airports like London Heathrow and Shannon. These hubs have installed advanced CT scanners (similar to medical grade) that can create a 3D image of the bag's contents and "digitally unpack" liquids, allowing them to detect explosive signatures even in large volumes. Until these scanners are universal, the 100ml rule remains the international fallback to ensure consistent safety across all borders.