Nickel skin levels in different occupations and an estimate of the threshold for reacting to a single open application of nickel in nickel-allergic subjects

Background Nickel is a frequent allergen throughout the world. However, the extent to which nickel is relevant as an occupational contact allergen as opposed to being simply a reflection of jewellery exposure has been unclear. Some thresholds for cutaneous nickel exposure to induce a dermatitis reaction in nickel-allergic individuals have been defined. Over recent years it has become possible to measure accurately the quantity of nickel on the skin of individuals in a number of occupations. Objectives To measure the quantities of nickel on the skin of the fingers in workers employed in occupations for which nickel has been suspected as a contact allergen. To define the threshold for a dermatitis reaction after the single application of a quantity of nickel to the skin of nickel-allergic individuals when read at 2 days. Methods We employed the 'finger immersion' technique for sample collection and induction coupled plasma mass spectrometry for the nickel measurement. Nickel platers, cashiers, sales assistants, caterers, healthcare assistants, office workers, dental nurses and hairdressers were studied (five in each group except for seven cashiers). A correction was made for the fact that the finger immersion method underestimates the amount of nickel on the fingertip. The threshold for reactivity to a single application of nickel was studied by the application of various concentrations of nickel (mu g cm(-2)) [0.05 (two subjects), 0.5 (two subjects), 2.5 (three subjects), 5.0 (21 subjects), 15 (19 subjects), 30 (19 subjects) and 45 (18 subjects)] in 21 subjects overall using Finn chambers on forearm skin. The reading was made at 2 days and reactions were graded using the International Contact Dermatitis Research Group classification. Results Nickel levels on the fingers of platers, cashiers, sales assistants, caterers, and even office staff, were at or above the 0.035 mu g cm(-2) level at which 22% of nickel-allergic subjects will react (after applying a correction). The single open application of nickel study demonstrated a dose-response relationship, with no subjects reacting to <= 2.5 mu g cm(-2), but increasing numbers reacting at the higher concentrations as follows: six of 21 (28%) at 5.0 mu g cm(-2), six of 19 (31%) at 15 mu g cm(-2), seven of 19 (37%) at 30 mu g cm(-2) and 11 of 18 (61%) at 45 mu g cm(-2). Conclusions This study confirms that nickel levels on the skin in coin handling occupations and some others are sufficient to induce an allergic contact dermatitis in some nickel-allergic subjects. A single application of 5 mu g cm(-2) when read at 2 days induced a dermatitis reaction in six of 21 nickel-allergic subjects.