We examined ROS generation induced by blue light irradiation in P. gingivalis. The P. gingivalis suspension containing 20 µM CellROX ® Green Reagent was irradiated with blue light. While ROS levels were significantly higher in the 100J blue light irradiation group compared with the non-irradiated (0J) group, there was no difference between the 0, 1, and 10J blue light irradiation groups (Fig. 5A). As shown in Fig. 5B, the oxidative stress levels of P. gingivalis DNA at 100J of blue light irradiation had significantly higher 8-OHdG levels compared with the non-irradiated (0J) group.Figure 5Oxidative stress induced by blue light irradiation of P. gingivalis. (A) ROS generation levels upon blue light irradiation in P. gingivalis. (n = 3) †Significant difference (p < 0.0001). (B) Generation of 8-OHdG upon blue light irradiation of P. gingivalis (n = 3) *Significant difference (p < 0.05).