Substances that are applied to the skin to heal it, make it feel better or improve its appearance, have much in common. They can all do damage to the skin as well as perform the task for which they were designed. They and the substances they contain are all absorbed through the skin to a greater or lesser extent. In addition, all these agents are constructed in the same general way. For these reasons it seems odd and uneconomical to consider topical pharmaceuticals, toiletry products and cosmetics separately. This was the reasoning behind the holding of a small symposium of workers involved with one or another aspect of the formulation of substances destined for application to the skin. Several aspects of the subject are covered in this book which is based on the symposium and the contents should be of interest to all who are concerned with the prescription, assess­ ment or formulation of topical agents. 9 1 Acne Caused and Treated by Topical Agents W. J. CUNLIFFE The four main aetiological factors involved in the development of l acne are (1) an elevated sebum excretion rate ; (2) ductal hyper­ 3 keratinization 2; (3) an abnormality of microbial function ; (4) host 4 inflammatory response • Although opinions differ on both sides of the Atlantic, most authorities in the United Kingdom believe that increased sebum excretion rate is the main drive to acne, there being a definitive relationship between the severity of the acne and the seborrhoea of this disease.