Nothing slows down a checkout line quite like a cashier scanning the same item four times before giving up and typing the price manually. Most scan failures trace back to one of a handful of causes — worth checking in this rough order.
The print quality has degraded
Thermal labels fade over time, especially with heat or sunlight exposure, and once the contrast drops too low, scanners simply can't read the bars anymore. If old stock suddenly stops scanning while new stock works fine, this is almost always the reason.
The barcode is printed too small for the scanner's distance
A barcode sized for a close-range handheld scanner may not scan reliably if staff are holding it further away, or vice versa. Check the size against how your specific scanner is actually being used on the floor, not just the spec sheet.
There's damage or a fold across the bars
A crease, a sticker overlap, or a scuff running across the barcode — rather than along its length — breaks up enough of the pattern that scanners give up. Bars can tolerate some damage running parallel to them, but almost none running across.
The wrong symbology is selected on the scanner
Some scanners are configured to only read specific barcode types by default. If a code that should work still won't scan, check the scanner's settings to confirm the format you're using (EAN13, Code128, etc.) is actually enabled.
The quiet zone got trimmed off
If a label was cut or resized and the blank margin around the barcode disappeared, scanners lose their reference point for where the code starts and ends. This is a common issue with labels resized to fit a smaller product than originally planned.