Conflicts of interest: D.O. has been a speaker and/or consultant for AbbVie, LEO Pharma, UCB, Bristol Myers Squibb and Boehringer Ingelheim. R.B. has received support for attending meetings and/or travel for AbbVie, Amgen, LEO Pharma, Eli Lilly, Novartis and Sanofi. M.B. acted as a speaker or consultant for AbbVie, Eli Lilly, Janssen, LEO Pharma, UCB, Novartis, Bristol Myers Squibb and Boehringer Ingelheim. G. Caldarola has received honoraria as speaker and consultant for AbbVie, Almirall, Biogen, Eli Lilly, LEO Pharma, Novartis, Janssen, Sanofi, Pfizer, and UCB Pharma. A. Campanati has served as a speaker, consultant or advisory board member for AbbVie, Almirall, Amgen, Eli-Lilly, LEO Pharma, Janssen-Cilag, Novartis, Pfizer, Sanofi-Aventis, Boehringer Ingelheim and UCB Pharma. E. Campione has served as an advisory board member, received fees for lectures and/or research grants by Almirall, Amgen, AbbVie, Bristol Myers Squibb, Incyte, LEO Pharma and UCB. A. Carugno has been a speaker and/or consultant for Almirall, Amgen, AbbVie, Boehringer Ingelheim, Eli Lilly, LEO Pharma, Janssen-Cilag, Novartis and UCB Pharma. A. Costanzo has been a consultant and/or speaker for AbbVie, Almirall, Amgen, Janssen, LEO Pharma, Eli Lilly, Galderma, Boehringer Ingelheim, Novartis, Pfizer, Sandoz and UCB. E. Cozzani has acted as a speaker or consultant for AbbVie, Almirall, Eli Lilly, LEO Pharma and Novartis. G.DalB. has been consultant for AbbVie, Eli Lilly, Janssen, Sanofi, UCB and Novartis. A.D. has served as a speaker, consultant or advisory board member for AbbVie, Almirall, Amgen, Eli Lilly, LEO Pharma, Janssen, Novartis, Boehringer Ingelheim and UCB Pharma. M.E. has served as speaker/consultant for AbbVie, Amgen, Almirall, Eli Lilly, Janssen, LEO Pharma, Novartis, Pfizer, Sanofi and UCB. M.C.F. has served on advisory boards, received honoraria for lectures and/or research grants from AMGEN, Almirall, AbbVie, Boehringer Ingelheim, BMS, Galderma, Kyowa Kyrin, Incyte, LEO Pharma, Pierre Fabre, UCB, Eli Lilly, Pfizer, Janssen, MSD, Novartis, Sanofi, Regeneron and Sun Pharma. C.G. has received consultation fees and/or grants for research projects, advisory panels and giving educational lectures from Wyeth-Pfizer, Abbott Immunology-AbbVie, Janssen-Cilag, Novartis, LEO Pharma, LEO Pharma Denmark, Ely-Lilly, Celgene, Merck-Serono, UCB Pharma, Sanofi-Aventis, Amgen and Almirall. P.M. has been a speaker for AbbVie, Lilly, Novartis, Janssen-Cilag, Celgene, LEO Pharma and Almirall. A.N. has served on advisory boards, received honoraria for lectures and research grants from Almirall, AbbVie, BMS, LEO Pharma, Celgene, Eli Lilly, Janssen, Novartis, Sanofi-Genzyme, Amgen and Boehringer Ingelheim. The other authors declare no conflicts of interest.