Nickel: the search for alternative, optimal and non-irritant patch test preparations: Assessment based on laser...

Several contact allergens including nickel are also irritants. Ideal patch test preparations should not miss cases of contact allergy and should be non-irritant. The currently used nickel preparation (5% nickel sulfate in petrolatum; 0.19 m) is a compromise. The present aim was to compare the skin-irritant potential of various nickel preparations (sulfate, chloride, nitrate in petrolatum and in water) by using the objective, noninvasive laser Doppler technique for assessment.

Preparations with various nickel concentrations and vehicle controls were applied under occlusion (Finn chambers) on the volar forearms of healthy subjects for 48 h. The test sites were examined visually and measured with a laser Doppler flowmeter before, and repeatedly after, removal of test patches. Some preparations were also used when patch testing consecutive dermatitis patients.

0.19 m nickel chloride and nickel nitrate in petrolatum caused erythema as well as increase in skin blood flow, while lower concentrations (0.10, 0.05 and 0.01 m) did not affect skin blood flow. At higher concentrations the sulfate was less reactive than the other salts. The reactivity was more pronounced with the salts in petrolatum than in water. 0.05 m nickel nitrate was equivalent to 0.19 m nickel sulfate in diagnosing contact allergy in patch testing, while 0.30 m nickel sulfate in water missed several cases.

The laser Doppler technique is more sensitive than the naked eye and can indicate nickel patch test preparations with marginal irritant properties. Some promising alternative candidates have been identified.