CONTACT DERMATITIS AND ALLERGY DOI 10.1111/j.1365-2133.2005.06430.x Additive impairment of the barrier function by mechanical irritation, occlusion and sodium lauryl sulphate in vivo J.W. Fluhr, A. Akengin, A. Bornkessel, S. Fuchs, J. Praessler, J. Norgauer, R. Grieshaber,* P. Kleesz* and P. Elsner Skin Physiology Laboratory, Department of Dermatology and Allergology, Friedrich-Schiller-University, Erfurter Str. 35, 07740 Jena, Germany *Institution for Statutory Accident Insurance and Prevention in the Food Processing Industry and Catering Trade (BGN), Mannheim, Germany Correspondence Joachim Fluhr. E-mail: fluhr@derma.uni-jena.de Accepted for publication 2 September 2004 Key words: detergent, irritant contact dermatitis, mechanical irritation, stratum corneum hydration, tandem irritation, transepidermal water loss Conflicts of interest: none declared. Summary Background The interaction between potential irritants in the workplace might be important because workers are not usually exposed to a single irritant, but to multiple potentially harmful substances. Physical irritant contact dermatitis caused by friction or mechanical abrasion is a common occupational dermatosis. Pro- longed water exposure by occlusion is also common in the workplace. Several studies have revealed the negative effect of the common anionic detergent sodium lauryl sulphate (SLS) on permeability barrier function. Objectives To study the additive impairment of permeability barrier function by mechanical irritation combined with 0Æ5% SLS or prolonged water exposure by occlusion, as models of mild irritation. Methods The volar forearms of 20 healthy volunteers were exposed to mechanical irritation and occlusion with water or 0Æ5% SLS for four consecutive days in a combined tandem repeated irritation test (TRIT). Permeability barrier function was measured with a Tewameter TM 210 Ò . Irritation was assessed with a Chromameter CR 300 Ò and a visual score. Results Barrier disruption in our model was rated as follows: occlusion with SLS and mechanical irritation > occlusion with SLS > occlusion with water and mechanical irritation > mechanical irritation and occlusion with water > occlu- sion with a glove and mechanical irritation > mechanical irritation > occlusion with water. Barrier disruption caused by occlusion or mechanical irritation was enhanced by the tandem application. The choice of irritant under occlusion, time of occlusion and order of tandem application all affected the degree of barrier disruption. Evaporimetry was able to detect early stages in the development of an irritant reaction before it became visible. Chromametry was not able to detect this early response. Conclusions Physical irritants (friction, abrasive grains, occlusion) and detergents such as SLS represent a significant irritation risk and should be minimized, espe- cially when acting together, as shown in our TRIT model. Mechanical irritation is common in the workplace. However, few studies have focused on this factor. No data are available from studying mechanical irritation in a standardized model. Tape stripping as a model for removal of stratum corneum (SC) layers has been used for many years. 1 Sequential removal of SC layers results in a loss of permeability barrier function and subsequently leads to a coordinated barrier repair. 2–4 It has been shown that acute barrier disruption by tape stripping results in release of a preformed epidermal pool of cytokines that coordinate the restoration of the cutaneous permeability barrier. 5 Our group has developed a standardized approach to assess irritation in conditions approaching those in the work- place, using a tandem repeated irritation test (TRIT). 6–8 With this model we were able to show that sequential (‘tandem’) application of different irritants modifies the cutaneous response, in contrast to repeated exposure to each irritant alone, indicating an aggravating or reducing effect of the com- bination of irritants. A standardized model for mechanical irritation which is dis- tinct from the usual tape stripping model is currently lacking. Furthermore, the models commonly used do not represent workplace conditions. Sodium lauryl sulphate (SLS) is one of Ó 2005 British Association of Dermatologists • British Journal of Dermatology 2005 153, pp125–131 125