1. Karolinska Institutet; Institute of Environmental Medicine; 171 77; Stockholm; Sweden
2. Department of Chemistry; KTH Royal Institute of Technology; 100 44; Stockholm; Sweden
3. Department of Dermato-Allergology; National Allergy Research Centre; Copenhagen University Hospital Gentofte; 2900; Hellerup; Denmark
4. St John's Institute of Dermatology; Guy's and St Thomas' NHS Foundation Trust; London; SE1 7EH; UK