What is the relevance of contact allergy to sodium metabisulfite and which concentration of the allergen should we use?

Background: The prevalence of contact allergy to sodium metabisulfite (SMB) has increased from the range of 1.4% to 1.7% to the range of 3.4% to 6.8% in published series over the past 20 years.
Aims: The aims of this study were to review contact allergy to SMB in our cohort and to investigate different concentrations to define the most appropriate concentration for patch testing.
Methods: Patient records were reviewed between February 2009 and December 2011 to obtain information on patient demographics, clinical presentation, and prevalence of contact allergy to SMB. Patients attending for patch testing, between January 2012 and June 2013, were tested with 3 strengths of SMB as part of the British standard series (1%, 0.1%, and 0.01%).
Results: Nine hundred ninety-six patients were patch tested to the British standard series including SMB 1% in petrolatum between February 2009 and June 2013, and 70 (7%) were positive. In the prospective group, 380 were tested to 3 concentrations of SMB (1.0%, 0.1%, and 0.01%). Fourteen patients (3.68%) had a positive patch test with 1% SMB, 7 to 0.1% SMB, and 3 to 0.01% SMB. There was exposure to SMB in 10 patients who cleared with avoidance at review 3 months later. The most frequent location of rash included face, hands, vulval, and perianal region.
Conclusions: Our study confirms reports of increasing prevalence of SMB allergy. A detailed review of exposure in the prospective study showed that SMB is relevant in most patients, and 1% in petrolatum is the best concentration for patch testing.