Moreover, polymorphism in several DNA repair genes, such as X-ray repair cross-complementing protein 1 (XRCC1), xeroderma pigmentosum group D 6 (XPD6) and 23 (XPD23), and cytochrome P450 1A1 (CYP1A1), was observed to be associated with high or medium DNA damage after exposure to air pollution [107]. This evidence concerns the gene CYP1A1 and xeroderma pigmentosum.