Based on an estimated sterilizing dose of 0.1 kJ m−2 222‐nm UVC (8) and a 10 000‐fold greater susceptibility to develop UV‐induced skin tumors in patients with XP in comparison with the general population (18), we set the dose of 222‐nm UVC per exposure for wild‐type with 5.0 kJ m−2 and for Xpa‐knockout mice with 0.5 and 1.0 kJ m−2. Here, XPA is linked to xeroderma pigmentosum.