CD03 Contact sensitization to shellac: a possible marker of fragrance allergy

Abstract

Shellac, the purified resin produced from the female lac bug (Kerria lacca), has its application within a wide range of industries, including healthcare, food, wood treatments and cosmetics. Shellac 20% alcohol is included in the British Society for Cutaneous Allergy/European Society of Contact Dermatitis extended facial series based on frequency of reactions exceeding the 0.3% threshold. However, the source of primary sensitization remains difficult to characterize through patch testing as relevance is not always clear and the test preparation has an irritant potential. We present a series of 28 patients from 2013 to 2022 with positive or irritant reactions to shellac, to elucidate its reaction pattern and relevance within our outpatient population. Cases with confirmed shellac positivity (‘+’ reactions and higher) or irritant reactions using a test preparation with alcohol 20% (Chemotechnique MB Diagnostics, Vellinge, Sweden) on days 2 and 4 of patch testing in a cosmetic series were retrieved between 2013 and 2022 from a total of 5458 people tested. Data collected from records included degree of positivity, irritancy, relevance, coexisting allergens, primary anatomical site and previous history of atopy. Data were processed using Microsoft Excel. We report 21 positive reactions, 14 (67%) of which were weak. Eleven (52%) positive reactions were deemed of current relevance, seven (33%) of doubtful relevance, one (5%) of past relevance and one (5%) a crossreaction to fragrance. Seven (25%) patients had documented irritant reaction to shellac. Nickel and colophony were the most common coexisting allergens in shellac-positive patients (positive in five and four cases, respectively). Nine (43%) cases with positive reaction had coexisting positivity of fragrance markers (which included one or more of geraniol, citral, Evernia furfuracea, turpentine, propolis, colophony, abitol, isoeugenol, cinnamyl alcohol, Jasminum officinale, jasmine absolute, majantole or benzaldehyde), indicating a higher prevalence than existing rates from studies in the general population. Fourteen (67%) positive cases documented the face as the primary site of disease, and 16 (76%) had a personal history of atopy. Our results indicate a significant association between shellac positivity and coexisting fragrance allergy, suggesting a role as a marker of fragrance allergy due to cross-reaction. When comparing irritant reactions to the proportion of positive reactions, this was higher than in previous US population-based reports (five irritant cases vs. 64 positive cases of a total cohort of 612 cases) but significantly lower than in a recent German population-based study (90 irritant cases vs. 76 positive cases of a total cohort of 2167), in all instances using the alcohol 20% preparation.