Marker-based reasoning has three points where it depends on information beyond the ingredient list itself, rather than breaking down entirely.
It depends on product type, for conditional markers. Sodium Benzoate’s ceiling is 0.5% in leave-on products and 2.5% in rinse-off, under Annex V entry 1 of Regulation (EC) No 1223/2009. An ingredient listed after Sodium Benzoate in a rinse-off product could still sit well above 1%. The 2.5% ceiling has already cleared the 1% ordering threshold. In a leave-on product, the same position reliably marks under 0.5%. The distinction resolves as soon as the product type is known, which for a reader holding the bottle is almost always immediate.
It estimates a range, not a point. Phenoxyethanol’s ceiling is 1.0%, but formulators commonly use it below that ceiling rather than at it. The marker sits somewhere under its legal maximum, and the label doesn’t say where. Position brackets an ingredient’s concentration. It doesn’t pin it down.
It says nothing about trace-level ingredients. Hyaluronic acid, tocopherol, and most peptides are formulated to function at small amounts by design. Their position relative to any marker carries no signal, whether they fall before it or after.
It needs a marker to be present at all. A formula with no fixed-ceiling preservative on the list gives the method nothing to locate and nothing to infer from.
None of these are failures of the method so much as its edges — the conditions under which it needs one more piece of information, or has none to work with. See What Makes a Concentration Marker Usable for which preservatives qualify as markers in the first place.
Read the full explainer: “How INCI List Position Works”
