Yellowing that appears in storage, rather than in wear, is usually a chemical reaction on the fabric surface. A well-known cause is phenolic yellowing, which ISO 105-X18 defines as discolouration caused by oxides of nitrogen acting with phenolic compounds. Packaging materials in contact with the fabric are a common place to look for those compounds, and marks often appear along folds or at contact points. Residues of softeners, optical brighteners or finishing chemicals on the fabric can also yellow with time, heat or light.

Look at the pattern of the marks

Marks along folds and at contact points with bags or board point to the packaging and the warehouse air. Even yellowing over the whole garment suggests a finishing residue or an optical brightener breaking down. Marks only on the outside of a stack suggest light or heat exposure. Photograph the pattern before washing anything.

Test the materials

A testing laboratory can screen the fabric for phenolic yellowing potential with ISO 105-X18. The standard notes it is a screening test specific to phenolic yellowing and does not cover other causes of yellow discolouration. Ask the factory what softener and finishing it used, and whether polybags and tissue are specified as low-phenolic. A wash test under a named procedure such as ISO 6330 shows whether the mark comes out, which helps decide whether the stock can be recovered.

Prevent it next time

Agree packaging materials with the factory, keep white stock away from engine exhaust and heat, rotate old stock first, and avoid sealing garments while still warm or damp. If the fabric goes through a colourfastness check such as ISO 105-C06, remember that test does not cover storage yellowing; it needs its own check.

Do not relabel affected goods with harsher care instructions to cover the problem. Care labels must reflect how the product can be safely cared for under the FTC Care Labeling Rule, 16 CFR Part 423.

If the stock is already affected, sort the cartons by how severe the marks are and test a few washed garments before deciding whether to rework, discount or write them off. Keep the affected polybags and cartons as evidence; they are what the laboratory will need. Tell the factory and packaging supplier promptly, with photographs and carton numbers, so they can check other orders packed with the same materials.