Vehicle-Controlled Effect of Urea on Normal and SLS – Irritated Skin

It is known that, depending on the concentration, treatment with urea could improve skin barrier function, despite its penetration-enhancing properties. This controversial skin effect of urea has been explored systematically in this study in terms of the effect of vehicle on the performance of urea. In the first part, a series of four semi-solid emulsions with 5% (w/w) urea, varying in the type of emulsion, nature of emulsifier and polarity of oil ingredients, have been evaluated with regard to their skin hydrating and transepidermal water loss (TEWL)-modifying properties. Placebo samples were tested alongside the urea-containing ones. Two best performing moisturisers from the above were chosen for the second part of the study, in which sodium lauryl sulphate (SLS)-irritated skin was treated with both placebo and urea-containing samples. In addition to TEWL and skin hydration level, the erythema index (EI) was measured before, during and after the treatment. The results have shown that barrier-improving and hydrating abilities of urea are bi-directional and dependent on both the type of vehicle used for its delivery and the state of skin.

Cosmetic science is a science-based, but fashion-led discipline. It covers a wide range of intersecting subjects, including biological sciences, dermatology, applied chemistry and physics.

The topic of this research cuts across dermo-pharmaceutical and cosmetic areas. Given its practical implications for both disciplines, a pharmaceutical journal, with its wider audience, was chosen for dissemination. This study is a part of the larger body of work carried out by the above international group (paper in Euro Cosmetics, Vol.10, issue 10, 2002 and 6 conference presentations). The over-arching research question was to establish how the formulation variables of topically applied products affect skin performance.

In particular, this paper explores the effect of the vehicle (four different cream formulations) on the moisturising efficacy of a topical active-urea. It has been noticed, in practice, that the skin moisturising effect of urea can vary, even when used in the same manner and in the same concentration, but the reason was not known. We have, for the first time, explored this phenomenon systematically, using two randomised in-vivo instrumental studies. One of them was performed at the London College of Fashion laboratory, under my direct supervision, and the second one at the Faculty of Pharmacy in Belgrade.

The results of both in-vivo studies have shown that the moisturising abilities of urea are bi-directional. This means that they are dependent on both the type of vehicle used for its delivery and the state of the skin. The findings of this study have both theoretical and practical implications, in terms of a better understanding of the skin behaviour and of more efficient formulation work, respectively.

Dr Slobodanka (Danka) Tamburic is a Reader in Cosmetic Science and a Programme Director for Cosmetic Science courses at London College of Fashion.

She has a background in Pharmacy, with an MSc in Pharmaceutical Technology and a PhD in Pharmaceutical Sciences. This was followed by three years of post-doctoral experience at the Centre for Materials Science, School of Pharmacy London. In the year 2000, she started the first graduate course in the UK solely devoted to the cosmetic industry - the BSc (Hons) in Cosmetic Science at London College of Fashion. Her current research encompasses the following strands:

* Exploring the efficacy of cosmetic products using skin bio-engineering methods (non-invasive in vivo testing)
* Evaluating internal structure of semisolid systems for cosmetic and pharmaceutical application and its effect on product efficacy
* Exploring the use of novel technology (especially nanotechnology) in cosmetics
* Biotechnological approach as a method for obtaining novel multifunctional cosmetic ingredients