1. Department of Occupational Medicine and Epidemiology, National Institute of Occupational Health, Oslo, Norway
2. Department of Chemical and Biological Work Environment, National Institute of Occupational Health, Oslo, Norway
3. Department of Dermatology, Oslo University Hospital, Oslo, Norway
4. Institute of Clinical Medicine, University of Oslo, Oslo, Norway
5. Regional Centre for Asthma, Allergy and Hypersensitivity, Department of Respiratory Medicine, Oslo University Hospital, Oslo, Norway