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A commonly occurring type of yellowing is described that typically takes the form of bright yellow patches or bands on the folded edges of nylon garments stored for long periods in cardboard boxes; it can also occur on other substrates and in other modes of storage not associated with cardboard. It can be distinguished from other types of yellowing by chemical and physical tests and is shown to be caused by the interaction of atmospheric nitrogen oxides with certain phenolic substances present in, for example, storage materials. The resulting compounds, which are almost certainly nitrated phenols, are colourless in acid media but yellow in alkaline; they can sublime in the acid form and migrate at room temperature through protective plastic films, to be fixed in the yellow, alkaline form on nylon fabric., or on other substrates contaminated by alkaline residues. In unbleached cardboard the phenolic precursors appear to be decomposition products of lignin. In the absence of cardboard the yellowing is attributed to other substituted phenols such as antioxidants that may have been added deliberately, or may be present as residual traces in, for example, dyed fabrics. The most likely source of nitrogen oxides is exhaust fumes from motor vehicles. Methods of preventing this type of yellowing are outlined.

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