Caroline Steel, a scientist and presenter of BBC's CrowdScience, has explained the real purpose behind airport security swab tests, revealing they are designed to detect explosive residues, not drugs. She shared her insights after experiencing a false positive herself before a flight.
How the Swab Test Works
Steel explained that the fabric swab is rubbed over surfaces like hands and bags to pick up microscopic particles. These particles are then placed inside an ion mobility spectrometer, where they are heated, turned into gas, and given an electrical charge to become ions. The ions travel through a tube with an electric field, moving at different speeds based on their mass, shape, and charge.
The device measures how long each ion takes to traverse the tube and compares that against a database of known substances. If an ion matches the speed of a suspicious compound, such as an explosive, the machine raises an alert.
False Positives and Common Misconceptions
Steel noted that although the test is highly sensitive, capable of detecting particles lighter than one trillionth of a gram, harmless substances can sometimes trigger alerts due to similarities in ion behaviour. In such cases, passengers simply undergo additional checks.
She clarified that the test is not for drugs, contrary to popular belief. One commenter responded: "I actually always thought it was for drug testing, but explosives do make sense for an airport." Another shared: "Happens to me just about every single time I fly and I've no idea why, always me out of 4-12 people I'm with." A third added: "I've been stopped nearly every time since having kids. One of the guys there told me some baby wipes set them off. Always have wipes in my bag, so it makes sense."
