Reactions of non-immunologic contact urticaria on scalp, face, and back

This study compared the reactivity of scalp, face, and back to nonimmunologic contact urticants (NICU) to ascertain relative responsiveness.

Model urticants, benzoic acid (BA) and hexyl nicotinate (HN) with 3 concentrations of each were applied to marked skin of 10 bald males during 6 weeks. One urticant was applied to one side of nasolabial fold, back, and scalp and the other applied to the contralateral side. Reactivity was assessed by visual scores (VS) and biophysical instruments. Subjects ranked skin sensation with a 10-point visual analogue scale.

With 0.25% HN application, upper back VS significantly (p<0.05) exceeded scalp and back VS also showed significantly (p<0.05) stronger reaction than face at 60 min post-application; however, at 2.5% BA site, VS of face exhibited significantly (p<0.05) higher than back at 15 min post-application but with 0.625% BA site, VS of back was significantly (p<0.05) higher than face. The a* value was significantly (p<0.05) higher on back than scalp with 0.625% BA treatment.

Thus symptoms and measurements vary among sites. Differences may be related to solubility related percutaneous penetration. We encourage investigation into this relatively neglected but clinically important arena, to help explain difference in consumer/patient acceptance of topical formulations.