Topical urea in skincare: A review

The worldwide incidence and prevalence of psoriasis is poorly understood. To better understand this, we performed a systematic review of published population-based studies on the incidence and prevalence of psoriasis. Three electronic databases were searched from their inception dates to July 2011. A total of 385 papers were critically appraised; 53 studies reported on the prevalence and incidence of psoriasis in the general population. The prevalence in children ranged from 0% (Taiwan) to 2.1% (Italy), and in adults it varied from 0.91% (United States) to 8.5% (Norway). In children, the incidence estimate reported (United States) was 40.8/100,000 person-years. In adults, it varied from 78.9/100,000 person-years (United States) to 230/100,000 person-years (Italy). The data indicated that the occurrence of psoriasis varied according to age and geographic region, being more frequent in countries more distant from the equator. Prevalence estimates also varied in relation to demographic characteristics in that studies confined to adults reported higher estimates of psoriasis compared with those involving all age groups. Studies on the prevalence and incidence of psoriasis have contributed to a better understanding of the burden of the disease. However, further research is required to fill existing gaps in understanding the epidemiology of psoriasis and trends in incidence over time.

Water is absolutely essential for the normal functioning of the skin and especially its outer layer, the stratum corneum (SC). Loss of water from the skin must be carefully regulated, a function dependent on the complex nature of the SC. The retention of water in the SC is dependent on two major components: (1) the presence of natural hygroscopic agents within the corneocytes (collectively referred to as natural moisturizing factor) and (2) the SC intercellular lipids orderly arranged to form a barrier to transepidermal water loss (TEWL). The water content of the SC is necessary for proper SC maturation and skin desquamation. Increased TEWL impairs enzymatic functions required for normal desquamation resulting in the visible appearance of dry, flaky skin. There have been recent discoveries regarding the complex mechanisms of skin hydration. In particular, it has been discovered that glycerol, a well-known cosmetic ingredient, exists in the SC as a natural endogenous humectant. Hyaluronan, which has been regarded mainly as dermal component, is found in the epidermis and is important for maintaining normal SC structure and epidermal barrier function. More importantly, the discovery of the existence of the water-transporting protein aquaporin-3 in the viable epidermis and the presence of tight junction structures at the junction between the stratum granulosum and SC have brought new insights into the mechanisms of skin water distribution and barrier function.