IVL Swedish Environmental Research Institute

Background: Cobalt (Co) causes allergic contact dermatitis (ACD) and the emerging use of Co nanoparticles (CoNPs) warrants gaining further insight into its potential to elicit ACD in sensitized individuals.

Objectives: The aims of the study were to clarify to what extent CoNPs may elicit ACD responses in participants with Co contact allergy, and to evaluate whether the nanoparticles cause a distinct immune response compared with cobalt chloride (CoCl2) in the skin reactions.

Methods: Fourteen individuals with Co contact allergy were exposed to CoNPs, CoCl2, a Co-containing hard-metal disc (positive control), and an empty test chamber (negative control) by patch testing. Allergic responses were evaluated clinically by a dermatologist at Days 2, 4 and 7. At Day 2, patch-test chambers were removed, and remaining test-substance and skin-wipe samples were collected for inductive-coupled plasma mass spectrometry (ICP-MS) analysis.

Additionally, skin biopsies were taken from patch-test reactions at Day 4 for quantitative real-time polymerase chain reaction analysis, histopathology and ICP-MS analysis of Co skin penetration.

Results: Patch testing with CoNPs elicited allergic reactions in Co-sensitized individuals. At all timepoints, clinical assessment revealed significantly lower frequencies of positive patch-test reactions to CoNPs compared with CoCl2 or to the positive control. CoNPs elicited comparable immune responses to CoCl2. Chemical analysis of Co residues in patch-test filters, and on skin, shows lower doses for CoNPs compared with CoCl2.

Conclusions: CoNPs potently elicit immune responses in Co-sensitized individuals. Even though patch testing with CoNPs resulted in a lower skin dose than CoCl2, identical immunological profiles were present. Further research is needed to identify the potential harm of CoNPs to human health.