Abstract
OBJECTIVE: The physiological skin surface pH is crucial for several epidermal barrier functions, like stratum corneum integrity, cohesion and restoration. Alterations of the “normal” acidic nature of the skin surface have been shown to correlate with specific skin conditions like aged or inflamed skin and are leading to impaired skin barrier function and formation. It is previously demonstrated that topical acidification in atopic dermatitis improves stratum corneum function, skin barrier structure and clinical signs in dermatitis. Against this background, we examined the impact of a slightly acidic skin care product containing urea on stratum corneum hydration, skin surface pH and epidermal barrier function in subjects with dry skin and atopic diathesis. METHODS: Stratum corneum hydration, skin surface pH and transepidermal water loss were biophysically measured before and after a 4-week treatment period with the test product (pH 4.5, 10% urea) compared to the reference product in 25 volunteers. In addition, dynamic epidermal barrier parameters like stratum corneum integrity, cohesion and recovery were investigated by using a previously described tape stripping approach. RESULTS: It was shown that the test product (pH 4.5, 10% urea) significantly elevated stratum corneum hydration and improved the acidic nature of the skin surface by lowering the skin surface pH to a greater extent compared to the reference product. After the 4-week treatment period a significant faster barrier restoration was detected on the test site treated with the test product compared to the reference product. Moreover, the test product strengthens the skin barrier integrity and cohesion. CONCLUSION: The present marketed skin care lotion was shown to increase epidermal barrier function after 4 weeks of application. Balancing and controlling the skin surface pH in subjects with dry and atopic-prone skin by application of the herein tested o/w emulsion with a given pH of 4.5, in combination with a 10% urea content seems to be effective and beneficial. The results are important for the formulation of topical products for dry and atopic-prone skin.
Highlights
The skin, or more precisely the epidermal permeability barrier (EPB), is the most important blockade to protect the human body from external influences [1] [2] [3]
We examined the impact of a slightly acidic skin care product containing urea on stratum corneum hydration, skin surface pH and epidermal barrier function in subjects with dry skin and atopic diathesis
It was shown that the test product significantly elevated stratum corneum hydration and improved the acidic nature of the skin surface by lowering the skin surface pH to a greater extent compared to the reference product
Summary
The skin, or more precisely the epidermal permeability barrier (EPB), is the most important blockade to protect the human body from external influences [1] [2] [3]. The main part of the EPB is formed by the stratum corneum (SC) This outer layer of the skin consists of corneocytes embedded in a highly organized lipid matrix and it is important for a proper skin permeability function [4] [5]. Besides the given skin barrier structure of proteins and lipids, the skin surface pH (ss-pH) and the individual cutaneous microbiome are important for an adequate EPB function [8] [9] [10] [11] [12]. Disturbances of these factors can trigger malfunction of the EPB function and moisture regulation, i.e. very dry and scaly skin, or even worse, skin diseases such as atopic dermatitis (AD) [13] [14] which is a common, multifactorial inflammatory disease associated with very dry, rough, itchy and inflamed skin [15]
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