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Author: Dr Ian Coulson, Consultant Dermatologist, East Lancashire NHS Trust, Lancashire UK. Copy edited by Gus Mitchell. October 2021.
Limonene and linalool are fragrance chemicals extracted from the peel of citrus fruits (limonene) and herbs, flowers, and woods (linalool).
Limonene and linalool are themselves occasional contact sensitisers. However, on exposure to oxygen in the air, both substances oxidise into hydroperoxides which are much more potent sensitisers. As such, limonene and linalool are an increasingly recognised source of allergic contact dermatitis.
Those sensitised may tolerate newly opened products, but after a period of time after the pack has been opened, the parent fragrance oxidises which can cause an allergic dermatitis. Due to this delayed oxidisation, a freshly opened product that is used daily at home may not cause problems, but an identical older opened product eg, those kept with holiday toiletries, may elicit a reaction.
Ten percent of individuals investigated for a suspected contact dermatitis were found to be allergic to these hydroperoxides. Allergy was more common in women and those aged over 40 years.
Patch testing confirms the diagnosis — hydroperoxides are included in some of the standard patch test series. Those sensitised will develop a positive patch result; tests are read 48 and 96 hours after application of the allergen to determine patch test reactions.
Patch testing details:
Offending products containing the hydroperoxides must be discontinued. The eczema is treated by the application of a topical steroid until the allergic reaction settles [see Allergic contact dermatitis].
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