The 26 fragrance allergens and which resins contain them

The 26 fragrance allergens are a fixed list of substances — 24 individual chemicals plus two natural extracts, oakmoss and treemoss — that the EU Cosmetics Regulation has required manufacturers to name on ingredient labels since 2005, whenever they exceed 0.001% in a leave-on product or 0.01% in a rinse-off one. The list exists because these substances are the most frequently confirmed causes of contact allergy in fragranced products, established through decades of patch-testing data. Several of them are not laboratory inventions at all: they occur naturally, sometimes at meaningful concentrations, in resins and balsams long used in perfumery and incense. Benzoin, Peru balsam, storax and Tolu balsam are the main contributors, because their chemistry is built from benzyl and cinnamyl esters that happen to sit on the allergen list. Frankincense, elemi and other terpene-rich oleoresins contribute a different allergen, limonene, through their essential-oil fraction.

What is the EU list of 26 fragrance allergens?

The list originates from a 2003 amendment to the EU Cosmetics Directive, later folded into Regulation (EC) 1223/2009. It names substances such as benzyl alcohol, benzyl benzoate, benzyl cinnamate, benzyl salicylate, cinnamal, cinnamyl alcohol, citral, citronellol, coumarin, eugenol, farnesol, geraniol, hexyl cinnamal, hydroxycitronellal, isoeugenol, limonene, linalool, methyl heptine carbonate, several synthetic ionones and cinnamaldehyde derivatives, and the two moss extracts. Labeling is triggered by concentration in the finished product, not by whether the substance came from a synthetic aroma chemical, an essential oil or a resin. A perfume built around benzoin absolute and one built around a synthetic base can each require the same disclosure if both cross the threshold for benzyl benzoate.

Which of the 26 allergens occur naturally in resins?

Not many, but the ones that do are common in the benzoin and balsam family. Benzyl alcohol and benzyl benzoate are present in both Siam and Sumatra benzoin, reflecting the styrax family’s characteristic benzyl-ester chemistry, discussed in more depth in Benzoin Chemistry. Benzyl cinnamate and cinnamyl alcohol turn up in storax and in Peru and Tolu balsam, where cinnamate esters are more prominent than in the styrax resins proper. Limonene is different in origin: it comes from the terpene fraction of oleoresins such as frankincense, elemi and galbanum rather than from balsamic esters, and it is one of the most widely distributed allergens on the list because it is common across citrus, conifer and Burseraceae essential oils generally.

Table: allergens with confirmed resin sources

What does benzyl cinnamate smell like, and why does storax contain so much of it?

Benzyl cinnamate on its own is faint, warm and slightly balsamic, closer to a soft vanilla-leather note than to anything sharp. Storax, the resin of Liquidambar orientalis and Liquidambar styraciflua, produces it because the tree channels a large share of its resin acids into cinnamic-acid esters rather than the benzoic-acid esters that dominate true benzoin. That biochemical difference is also what separates storax from benzoin in scent: storax reads leathery and slightly animalic, while Siam benzoin leans toward vanilla and Sumatra benzoin toward cinnamon-tinged balsam, a contrast covered in What Does Benzoin Smell Like?.

Why do balsamic resins carry more allergens than clear resins like frankincense?

The styrax and Myroxylon balsams are essentially thick suspensions of aromatic esters and free acids — benzoic acid, cinnamic acid, benzyl alcohol, benzyl and cinnamyl esters — precisely the chemical class the 26-allergen list was built to cover. Frankincense, elemi and mastic, by contrast, are largely terpene- and boswellic-acid-based; their allergen exposure comes almost entirely through limonene and, to a lesser extent, other monoterpenes, which oxidize on air exposure and increase sensitizing potential over time. This is one reason old, oxidized citrus and conifer oils are considered more allergenic than fresh ones, while benzoin’s ester profile stays comparatively stable with age, a point explored in We Aged Benzoin for a Year Four Ways.

How are these allergens declared on a label?

Once a resin-derived material is dosed into a finished fragrance or cosmetic above the EU threshold, each qualifying allergen must be named individually in the ingredient list, in addition to any general fragrance or parfum declaration. A perfumer working with benzoin absolute, Peru balsam or storax therefore needs to calculate not just the total resin dose but the resulting concentration of benzyl alcohol, benzyl benzoate and benzyl cinnamate individually, since each carries its own threshold. This calculation sits alongside IFRA restriction limits, which independently cap several of these same materials for sensitization risk; both frameworks are discussed together in Diluting Resins for Perfumery and in Benzoin Safety.

Does “natural” mean safer than synthetic here?

No. The EU list treats a molecule the same regardless of origin: benzyl benzoate isolated from Tolu balsam and benzyl benzoate produced industrially from benzyl alcohol and benzoic acid are the same compound and trigger the same labeling rule. What differs between a whole resin and an isolated allergen is the surrounding matrix — a natural balsam brings its allergenic esters bundled with dozens of other trace constituents, some protective, some additive, which is part of why regulators size thresholds against the whole finished product rather than against any single raw material’s reputation.

What this means when buying resin-based perfumes

Anyone with a known sensitivity to balsam of Peru, one of the most frequently positive results in patch-testing series, should expect cross-reactivity with benzoin, Tolu balsam and storax, since all four share benzyl benzoate, benzyl cinnamate and related esters. This does not make the resins interchangeable in scent, only in allergen profile: Siam benzoin and Peru balsam smell markedly different despite the chemical overlap. Reading a label’s named allergens, rather than relying on the word “benzoin” or “balsam” alone, remains the more reliable way to judge exposure risk.

• perfumery
• allergens
• regulation
• benzoin
• resin-chemistry