Our discovery that arginine deficiency inhibits the proliferation of hair matrix and, consequently, hair growth by ROS‐mediated mTOR signaling inhibition bears resemblance to observations made in cancer cells.[79] Although the promotion effect of the mTOR signaling pathway on the activation of HFSCs in mice has received significant attention,[80] its role in human HFs remains poorly understood. The gene discussed is MTOR; the disease is cancer.