**1. Introduction**

Psoriasis is a chronic immune cell-mediated inflammatory skin disease characterized by the formation of scaly indurated erythema occurring most commonly on the elbows, knees, scalp, and lower back, but any skin surface can be involved [1]. The highly visible condition greatly affects people's quality of life that can be stigmatizing. People with psoriasis are at an increased risk of developing other chronic and serious health conditions. Comorbidities include psoriatic arthritis, inflammatory bowel disease, hypertension, diabetes, obesity, and depression. The worldwide prevalence of psoriasis is estimated to be 2–4%, rising up to 9.7% in Scandinavian countries [2, 3].

Psoriasis can be classified into mild, moderate, or severe disease according to the Psoriasis Area and Severity Index (PASI). Treatment choices are often based on the severity of disease: mild disease often managed with topical therapy, and moderateto-severe disease requiring systemic therapy for control, often with concomitant topical therapy [4–6]. Effects of systemic therapy in synergy with topical agents may help reduce the burden and achieve better quality of life that psoriasis patients deserve. In mild-to-moderate, as well as moderate-to-severe, psoriasis, 70–80% of patients start with topical agents and continue to use them with other active therapies.

Currently, high-potency topical glucocorticoid and vitamin D derivatives are the main treatments for psoriasis [7–9]. Topical glucocorticoids are effective but their use is limited to no more than 2–8 weeks due to their long-term side effects, such as atrophy [10]. This is particularly true in more sensitive areas, such as the face or intertriginous areas. There are numerous reports of low satisfaction for these topical agents [11]. Hence, there remains great unmet medical needs for developing a highly efficacious and safe topical treatment in psoriasis.
