Studies on Constituents of Moisturizers: Water-Binding Properties of Urea and NaCl in Aqueous Solutions

Abstract

A water content of about 10% in the horny layer is necessary for softness and pliability of this part of the epidermis. In conditions with dry skin, emollients of different types are used. It is important that solid data are collected about the effect of the ingredients of emollients and moisturizers. Urea has since long been used in the treatment of dry skin. In the present report, the mixture of urea and sodium chloride has been analyzed with respect to its effect on the water vapor pressure in concentrated solutions. The depression of the water vapor pressure by NaCl and urea was found to be additive. Thus, the decrease in water vapor pressure in aqueous solution of urea-NaCl mixtures can be estimated by adding the decrease of water vapor pressure caused by dissolving the pure compounds. The results indicate that urea and NaCl in aqueous solution do not interact strongly and are, therefore, compatible in moisturizing preparations. They can, therefore, both be expected to be effective in mixtures giving a better than one of them alone.

Do Urea and Sodium Chloride together Increase the Efficacy of Moisturisers for Atopic Dermatitis Skin?

“…Major factors accounting for this effect might be first hydration of the stratum corneum by increasing the water binding (urea) and second by absorbing and retaining moisture (hygroscopicity, NaCl). This accords well with the findings of Miettinen et al [5], who reported that the reduction in water vapour pressure by sodium chloride and urea was additive. On the basis of chemical studies of an aqueous solution, Miettinen et al [5] suggested that either sodium chloride or urea is effective in mixtures, but the effect is greater when they are used together.…”

“…Later improvements in moisturisers were made by Hagströmer/Nyrén/Emtestam adding active substances, such as urea, lactic acid and sodium chloride [3,4]. Recently, Miettinen et al [5], after analysing water vapour pressure reduction in vitro, have suggested that by adding NaCl and urea to a moisturiser, the combination might be more effective in this mixture than one of them alone. For a recent review on moisturisers, the chemistry and effects, please see Lodén and Maibach [6].…”

“…For a recent review on moisturisers, the chemistry and effects, please see Lodén and Maibach [6]. The findings of Miettinen et al [5] prompted us to study the effects of urea and sodium chloride in moisturisers on atopic skin. We used several recent non-invasive methods to characterise skin hydration objectively in a comparative, double-blind and randomised design.…”

Urea and Sodium Chloride in Moisturisers for Skin of the Elderly – A Comparative, Double-Blind, Randomised Study

“…Soluble hygroscopic substances in the natural moisturising factor cause hygroscopicity of the SC -i.e., the ability to absorb water [5]. Urea increases the waterholding capacity of the SC because it binds water [6]. Several clinical studies have indicated that moisturisers containing urea are useful for the treatment of dry or eczematous skin in atopic patients [1,7,10] and of hyperkeratotic skin [8,9,11,12].…”

“…Miettinen et al [6] suggested, on the basis of a reduction in water pressure in vitro, that urea and sodium chloride in aqueous solution have additive effects. Therefore, it was natural to start a clinical study to estimate the effect of a new combined moisturiser in such patients.…”