LAUSR

To the Editor: Li students tested with European cosmetic series Warshaw et al 2011–2012 4231 66 (1.6) All patch-tested patients tested with standard series Warshaw et al 2009–2010 4301 74 (1.7) All patch-tested patients tested with standard series Shellac is a purified form of resin produced byKerria lacca, an insect native to Asia. The resin produced by K. lacca has a gummy texture that hardens on exposure to air, protecting the larvae of the insect. Shellac is commonly used in both medical (eg, dental moldings, pharmaceutical coating) and nonmedical products (eg, sealants, edible glazes, furniture finishings). Multiple case reports and series have reported allergic contact dermatitis caused by shellac, and it was named an emerging contact allergen in 2011. However, few reports have evaluated the reaction rate and the reaction types in a larger series of patients. We examined the patch test results of patients between January 1, 2014, and December 31, 2016, who were tested with shellac at our institution's 3 sites. Testing was performed with shellac in a 20% concentration with alcohol (Chemotechnique MB Diagnostics AB, Vellinge, Sweden) as part of an extended standard/cosmetic series. Reactions were rated as irritant, macular erythema, weak (nonvesicular erythema, infiltration, or papules), strong (edema or vesicles), or extreme (bullous, ulcerative, or spreading lesions). From 2014 to 2016, shellac was tested on 612 (34.7%) of 1764 unique patients who underwent patch testing. Five patients (0.8%) had an irritant reaction. In addition, 64 patients (10.5%) had a positive reaction to shellac with reactions graded as weak (n = 57 [9.3%]), strong (n = 7 [1.1%]), or extreme (n = 0 [0.0%]). A further 70 patients (11.4%) had reactions graded as macular erythema; these reactions were excluded from the calculation of positive reaction rates. Overall, our reaction rates are significantly greater than the reaction rates found in previous population-based reports (Table 1). Although it has been reported that shellac in alcohol tends to be a common irritant, we found shellac to have a relatively low irritant rate (0.8%).