Fragrance allergens: limonene and linalool

Why they are named separately

EU cosmetics regulation requires twenty-six specific fragrance substances to be declared by name on the label when present above 0.001% in leave-on products or 0.01% in rinse-off products. The list exists because these substances are established contact allergens with sufficient prevalence to warrant informing consumers.

In the Youlief Cleansing Serum Niacinamide, limonene appears at 0.0263% and linalool at 0.0108%, both above the rinse-off threshold, which is why they are itemised. The Collagen variant carries 0.2% fragrance with no allergens itemised - meaning any of the twenty-six present fall below threshold.

What is Fragrance allergens: limonene and linalool?

Limonene is a monoterpene from citrus peel, giving a fresh citrus note. Linalool is a monoterpene alcohol found in lavender, coriander and many flowers. Both occur naturally in essential oils and both are also produced synthetically. Neither is added as an allergen; both are ordinary fragrance and flavour materials that happen to be sensitisers in susceptible people.

The oxidation detail that matters

Neither limonene nor linalool is a strong sensitiser in its pure state. Both auto-oxidise on exposure to air, and it is the oxidation products - hydroperoxides - that are the significant allergens. This is why older products and poorly packaged ones present more risk, and why antioxidant systems in fragranced formulations are not just about scent stability.

What the declaration does not mean

It is not a toxicity warning and not a statement that the product is unsafe. It concerns sensitisation potential in a minority of people, most of them already sensitised. For the majority these substances are unremarkable.

It is also worth noting the related point on the crop side: geraniol, an active ingredient in several Vegalab crop products, is on this same list of twenty-six. The same molecule can be a pesticidal active in one context and a declarable fragrance allergen in another, and readers arriving from either direction deserve the full picture.