Limonene
Limonene is a citrus-scented compound found in many essential oils and added as fragrance. It is one of the fragrance allergens the EU requires to be named on the label, and once oxidised by air it becomes a stronger skin sensitiser — so it is flagged for fragrance allergy and sensitive skin.
Limonene occurs naturally in citrus-peel oils and is widely used to give products a fresh scent. On its own it is a weak sensitiser, but on exposure to air it oxidises into hydroperoxides that are considerably more allergenic.
It is one of the fragrance substances listed in Annex III of EU Regulation 1223/2009 that must be declared by name above 0.001% in leave-on and 0.01% in rinse-off products. People who patch-test positive to oxidised limonene should avoid it; it can also irritate sensitive or eczema-prone skin.
Who this affects
Caution
- Fragrance allergy: A labelled EU fragrance allergen; oxidised limonene is a known contact sensitiser.
- Sensitive skin & eczema: A common fragrance-derived irritant for reactive skin.
Frequently asked questions
Limonene is a fragrance terpene that gives a fresh citrus scent, extracted mainly from the peel of citrus fruits though it can also be produced synthetically. It is very widely used in cosmetics, personal-care products and household cleaners. DermNet describes it as a fragrance chemical extracted from citrus peel.
Limonene is one of the fragrance allergens the EU requires to be named individually rather than hidden under "parfum." Under Regulation (EU) 2023/1545 (amending Regulation (EC) No 1223/2009) it must be declared when its concentration exceeds 0.001% in leave-on products or 0.01% in rinse-off products, so consumers who react to it can spot it.
Pure limonene is only a weak sensitiser, but it can cause allergic contact dermatitis, especially once oxidised. DermNet reports that about 10% of people investigated for suspected contact dermatitis test positive to the hydroperoxides of limonene and linalool, with allergy more common in women and people over 40. Patch testing by a dermatologist is how it is confirmed.
Yes. On exposure to air, limonene oxidises into hydroperoxides that DermNet describes as "much more potent sensitisers." This is why a freshly opened product may be tolerated while the same product used long after opening can trigger a reaction. It is the oxidation products, not fresh limonene, that are the main concern.
Most people tolerate limonene, but because it is a recognised fragrance allergen that becomes a stronger sensitiser once oxidised, those with sensitive or eczema-prone skin may prefer to avoid it or choose fragrance-free products. This is general information, not medical advice; only patch testing by a dermatologist can confirm a true allergy, and the label is authoritative for whether limonene is present.