|English: 2+ patch test reaction (Photo credit: Wikipedia)|
"Polysensitisation" (PS) is usually defined as contact sensitisation to 3 or more unrelated haptens of the baseline patch test series. It is debatable whether the PS phenotype represents a distinct genotype or a natural staggered progression from a uni to oligo to polysensitisation process. Statistical modelling for identifying risk factors for this ill defined PS phenomena to 3 or more ‘unrelated’ haptens is difficult. Bivariate analysis and logical regression models were unsatisfactory.
This recent article  in BJD explores the concept of Polysensitisation (PS) in contact dermatitis using an interesting and novel methodology using a colossal central European dataset of about 140,000 patch test results. They have used a negative binomial hurdle regression method for count data to independently estimate risk to be sensitised at all and the risk of having several contact allergies, i.e., to be polysensitised.
The axillae and the feet were found to be strong PS risk factors along with increasing age and female sex. In comparison, atopic eczema and occupational dermatitis were less important risk factors.
The size of their dataset and the novel methodology makes this the most authoritative study of this unique phenomenon.
Special thanks to Dr. Wolfgang Uter and the rest of the team for the details.
1. OD - CoD - http://gulfdoctor.net/acd/ (Object Database for Contact Dermatitis)
2. Schwitulla, J et al. "Risk factors of polysensitisation to contact allergens." British Journal of Dermatology (2013). http://onlinelibrary.wiley.com/doi/10.1111/bjd.12423/abstract