The efficacy and safety of Longmu Tang granule for the treatment of atopic dermatitis: study protocol for a single-centred, double-blinded, randomised, placebo-controlled trial oleh Ya-qin Li, Tao-tao Shen, Qing-ying Wang, Meng-xi Ma, Feng-yan Tian, Yuan-yao She, Yi-cheng Tao, Jing-jing Wang, Hui-yan Chi, Na Lang, Jian-xun Ren