The combination of CO2 and Q-switched alexandrite lasers has produced better results than the Q-switched alexandrite laser alone. In a study done in Thailand, six women were treated on one side of the face with combined ultrapulse CO2 laser and Q-switched alexandrite laser, and on the other side with the Q-switched alexandrite laser alone. The combination of lasers produced a superior and significant reduction in pigmentation, as compared with the single laser (45,46). However, an increase in undesirable side effects,
including PIH, was also seen. Some authors believe that treatment with hydroquinone and retinoic acid prevents PIH after treatment with CO2 laser (47,48).