Epidemiology, management and the associated burden of mental health illness, atopic and autoimmune conditions, and common infections in alopecia areata: protocol for an observational study series - Harries, M; Macbeth, AE; Holmes, S; Thompson, AR; Chiu, WS; Gallardo, WR; Messenger, AG; Tziotzios, C; de Lusignan, S (BMJ Open, 2021)