Figure 5 Diagnostic tools to validate and differentiate alopecia areata Part b is reproduced with permission from Messenger, A. G., Sinclair, R. D., Farrant, P. & de Berker, D. A. R. in Rook’s Textbook of Dermatology 9th edn (eds Griffiths, C., Barker, J., Bleiker, T., Chalmers, R. & Creamer, D.) 89 (Wiley-Blackwell, 2016), Wiley. Part c is adapted with permission from Messenger, A. G., Slater, D. N. & Bleehen, S. S. Alopecia areata: alterations in the hair growth cycle and correlation with the follicular pathology. Br. J. Dermatol. 114, 337–347 (1986), Wiley Pratt, C. H. et al. (2017) Alopecia areata Nat. Rev. Dis. Primers doi:10.1038/nrdp.2017.11