The variation in nickel reactivity as shown in this article is of great importance and should be kept in mind when a patient has a positive history of allergic contact dermatitis but negative patch test results to nickel.

Concomitant patch test reactions to nickel and palladium have frequently been reported in patients undergoing investigation because of suspected allergic contact dermatitis. Theoretically, these reactions can be explained by multiple, concomitant, simultaneous sensitization as well as cross-sensitization. We studied whether concomitant reactions to nickel and palladium could represent cross-sensitization in females hypersensitive to combinations of nickel, palladium and cobalt. Females were patch tested with serial dilutions of nickel sulfate, cobalt chloride and palladium chloride on the upper back. 1 month later, when the patch test reactions were gone, the patients were randomized into 2 groups that were challenged orally with either nickel or placebo. 1 day later, the areas of previous positive patch test reactions were read in a blind way looking for flare-up reactions. Nickel provocation but not placebo yielded flare-up reactions on sites previously tested with nickel (P = 0.012) and palladium (P = 0.006), but were also observed on sites previously tested with cobalt, even though this was not statistically significant. Flare-up reactions of previous patch test reactions to nickel and palladium after oral challenge with nickel speak in favour of a cross-reactivity mechanism.

There was a statistically significant association between contact allergy to aluminium and persistent subcutaneous nodules in children who had had hyposensitization therapy.

The concentration of released cobalt was high enough to elicit allergic contact dermatitis in cobalt-sensitized patients. As the materials in the discs are used in wear parts of hard metal tools, individuals with contact allergy to cobalt may develop hand eczema when handling such materials.

Several factors, such as amount of allergen, vehicle, anatomic site, immunologic status and previous eczema, may influence delayed hypersensitivity reactions. In an extended model, we have studied the significance of previous allergic contact dermatitis for elicitation of delayed hypersensitivity to nickel in 25 nickel-allergic females. On 3 occasions, 8, 4 and 1 months before the final challenge patch testing, an experimental allergic contact dermatitis from nickel was induced on the lower back. At the challenge patch testing, 4 identical dilution series of nickel were tested on 4 areas on the lower back 3 with previous but healed dermatitis and 1 control area. The tests were read in a blind way. A significantly higher test reactivity was found at the areas with a previous allergic contact dermatitis, the shorter the time interval between the previous provocation and the challenge, the stronger the reaction. These results may be of importance for the understanding of factors contributing to chronicity of allergic contact dermatitis.

Over a short period of time, there was an outbreak of work-related skin lesions among workers at a company producing flooring laminate boards, after the introduction of a water-repellent lacquer based on diphenylmethane-4,4'-diisocyanate (MDI). In 5 workers, patch testing was performed with a standard series, an isocyanate series and work-environmental products when indicated. 3 of the workers were tested with the lacquer, and contact allergy was found with concurrent reactions to 4,4'-diaminodiphenylmethane (MDA). 1 of the 3 workers also showed a simultaneous reaction to MDI, whereas 1 showed a positive reaction to dicyclohexylmethane-4,4'-diisocyanate (HMDI). Of the 2 individuals not tested with the lacquer, 1 reacted to both MDI and MDA, whereas the other reacted to a soap used at work. In 3 of 4 cases, the isocyanate reactions appeared after D3. Occupational contact with isocyanates should not exclusively be focused upon respiratory hazards, as this report shows that skin contamination probably increases the risk of developing contact allergy to isocyanates and isocyanate-related substances. When aiming at diagnosing contact allergy to isocyanates, it is desirable to perform a late reading, as positive reactions appear late. MDA appears to be a good marker for isocyanate hypersensitivity.

The results of this study indicate that patch testing with aluminium chloride hexahydrate 2.0%, with an empty Finn Chamber® and the intradermal test with the salt and doses used are insufficient methods to detect contact allergy to aluminium. Aluminium chloride hexahydrate at 10.0% gave the highest number of positive reactions to aluminium.

Contact allergy to disperse dyes in textiles is documented in prevalence studies from southern Europe. To evaluate the prevalence of allergic patch test reactions to different textile dyes in southern Sweden, and to look at the sites of dermatitis in individuals hypersensitive to textile dyes, 3325 consecutively patch tested patients were retrospectively investigated. They had all been patch tested with the standard test series supplemented with a textile dye mix (TDM) consisting of 8 disperse dyes, i.e. Disperse (D) Blue 35, 106, and 124, D Yellow 3, D Orange 1 and 3, D Red 1 and 17. All but 3 of the TDM-positive patients were additionally tested with the separate dyes included in the mix. The frequency of contact allergy to TDM was 1.5 %, which is comparable with studies from southern Europe. The most common dye allergen was D Orange 1. The high prevalence of allergic reactions to D Orange 1 was unexpected, whereas test reactions to D Blue 106 and 124 were lower than expected from other studies. Compared to all tested patients, the TDM-positive patients more often had dermatitis on their arms, face, neck and axillary folds, and women also had a higher frequency of hand dermatitis.