CD03: Practical use of a limonene and linalool series

Siobhán McCarthy, Felicity Ferguson, Louise Cunningham, Ian White and John McFadden

St John’s Institute of Dermatology, London, UK

Contact allergy to oxidized limonene and oxidized linalool is common in the UK (Audrain H, Kenward C, Lovell CR et al. Allergy to oxidized limonene and linalool is frequent in the U.K. Br J Dermatol 2014; 171: 292–7) The hydroperoxide-containing forms tested are often irritant giving doubtful or equivocal results (Audrain et al.). Limonene and linalool are common components in essential oils, and present in many cosmetic and household products (Buckley DA. Fragrance ingredient labelling in products on sale in the U.K. Br J Dermatol 2007; 157: 295–300). We sought to determine the proportion of patients with positive patch tests to essential oils containing limonene and linalool, in patients with possible or definite reactions to limonene and linalool. All patients were tested to hydroperoxides of limonene 0·3% pet., and hydroperoxides of linalool 0·5% pet. and 1·0% pet. (Chemotechnique using IQ Ultra™) in a large tertiary referral service for cutaneous allergy as part of the baseline series. Limonene and linalool series were applied in those who had doubtful, equivocal or positive patch test reactions to limonene and/or linalool on day 2/3. The limonene series consisted of five essential oils: tea tree, geranium, lavender, neroli, eucalyptus and lemongrass. The linalool series consisted of six essential oils: ylang-ylang, geranium, jasmine, lemon and neroli. Results were collected over an 18-month period from July 2020 to December 2021, to determine the proportion of positive patch test results to these essential oils. Fifty-nine patients who had possible or positive reactions to limonene and/or linalool were tested to the limonene and/or linalool series over an 18-month period. Of the 46 tested to the limonene series, seven (15%) had a definite positive patch test reaction and one (2%) an equivocal result to one or more of the essential oils containing limonene. Positive tests were seen to tea tree oil in four, lemon grass oil in four, geraniol in two and neroli oil in two. Of the 27 tested to the linalool series, no patient had a positive patch test reaction to the essential oils containing linalool. Fifteen per cent of patients with positive, doubtful or equivocal reactions to limonene had positive reactions to one or more essential oils containing limonene. No patients with positive, doubtful or equivocal reactions to linalool had positive reactions to the linalool series suggesting little benefit from extended testing. The limonene series may be helpful in determining true positive reactions from irritant reactions to limonene in the baseline series.