Psoriasis and parapsoriasis en plaques are chronic inflammatory skin diseases, both representing therapeutic challenge in daily practice and adversely affecting the quality of life. Reactive oxygen species (ROS) has been evidenced to be involved in the pathogenesis of the chronic inflammatory diseases. We now report that molecular hydrogen water, an effective ROS scavenger, has significant and rapid improvement in disease severity and quality of life for patients with psoriasis and parapsoriasis en plaques. At week 8, our parallel-controlled trial revealed 24.4% of patients (10/41) receiving molecular hydrogen-water bathing achieved at least 75% improvement in Psoriasis Area Severity Index (PASI) score compared with 2.9% of patients (1/34) of the control group (Pc = 0.022, OR = 0.094, 95%CI = [0.011, 0.777]). Of patients, 56.1% (23/41) who received bathing achieved at least 50% improvement in PASI score compared with only 17.7%(6/34) of the control group (P = 0.001, OR = 0.168, 95%CI = [0.057, 0.492]). The significant improvement of pruritus was also observed (P = 3.94 × 10−4). Besides, complete response was observed in 33.3% of patients (2/6) of parapsoriasis en plaques and partial response in 66.7% (4/6) at week 8. Our findings suggested that molecular hydrogen-water bathing therapy could fulfill the unmet need for these chronic inflammatory skin diseases.