Patch testing for nickel allergy. The influence of the vehicle on the response rate to topical nickel sulphate.

A group of 43 patients with a clinical history of nickel allergy who exhibited an equivocal or no allergic reaction to a patch test at 48 h were further challenged using several different formulations of nickel sulphate. This experimental test battery comprised aqueous, dimethyl sulphoxide (DMSO) and propylene glycol (PG) solutions of nickel sulphate, and nickel sulphate incorporated into cetomacrogol cream and yellow soft paraffin (PMF). Although some of these vehicles were irritant, a formulation-dependent test response was observed, such that in terms of the number of responses per unit weight of nickel sulphate applied to the skin, the vehicles could be ranked: DMSO greater than PG greater than aqueous solution greater than cetomacrogol cream greater than PMF preparations. This ranking could be correlated with the relative ease with which nickel sulphate could be dialysed from each vehicle in vitro. This study demonstrates that for nickel sulphate, the vehicle can influence the outcome of patch testing apparently by modifying the quantity of nickel released into the skin for elicitation of the allergic response.