The North American Contact Dermatitis Group (NACDG) periodically reports allergen reaction rates and clinical significance. These results are not formally interpreted combining both components into one index.

The purpose of this study is to introduce the Significance-Prevalence Index Number (SPIN), which is a parameter that assesses the relative importance of different allergens.

Data was collected from published studies reported by NACDG from 1984 through 1996. The SPIN for each tested allergen was calculated as the product of the proportion of the population allergic by the weighted clinician-assessed likelihood of relevance of the reaction.

In the studies done in 1992 through 1996, fragrance mix, quaternium-15, balsam Peru, formaldehyde, thiuram mix, nickel sulfate, neomycin, bacitracin, carba mix, and paraphenylenediamine were the 10 leading allergens in clinical importance as measured by SPIN. Our SPIN calculations suggest that ethylenediamine and benzocaine have markedly decreased in clinical importance over the past decade, whereas methylchloroisothiazolinone/methylisothiazolinone has become a leading allergen. A number of allergens demonstrate high to intermediate SPIN, yet are not included in the T.R.U.E. test. These clinically important allergens include bacitracin, diazolidinyl urea, glyceryl thioglycate, ethyleneurea melamineformaldehyde, and imidazolidinyl urea.

SPIN allows clinicians to incorporate both the allergenicity and the relevance of the allergen into one measure.