Variation in aluminium patch test reactivity over time.

Background. Contact allergy to aluminium has been reportedmore frequently in recent years. It has been pointed out that positive patch test reactions to aluminium may not be reproducible on retesting. Objectives. To investigate possible variations in patch test reactivity to aluminium over time. Methods. Twenty-one adults, who had previously reacted positively to aluminium, were patch testedwith equimolar dilution series in pet. of aluminium chloride hexahydrate and aluminium lactate, four times over a period of 8 months. Results. Thirty-six of 84 (43%) serial dilution tests with aluminium chloride hexahydrate and 49 of 84 (58%) serial dilution tests with aluminium lactate gave negative results. The range of reactivity varied between a negative reaction to aluminium chloride hexahydrate at 10% and/or to aluminium lactate at 12%, and a positive reaction to aluminium chloride hexahydrate at 0.1% and/or to aluminium lactate at 0.12%. The highest individual difference in test reactivity noticed was 320-fold when the two most divergent minimal eliciting concentrations were compared. Conclusions. The patch test reactivity to aluminium varies over time. Aluminiumallergic individuals may have false-negative reactions. Therefore, retesting with aluminium should be considered when there is a strong suspicion of aluminium contact allergy.