CONTACT ALLERGY 485 MR. M. W. HINDLE: In the United Kingdom, I imagine, there is a great deal of over-the-counter buying of antihistamine creams for the treatment of certain urticarial rashes. Are there any dangers in this? THE LECTURER: It depends on the cause of the urticaria. If it is someone who gets midge bites or something similar, it will help, but otherwise I think the person should be consulting a doctor. MR. R. F. L. THOMAS: Have you come across any cases of members of the public who have developed an allergy after years of exposure to any particular material? Has there been any sign of repeated insult and slow loss of resistance by the body finally leading to the classical symptoms? THE LECTURER: This is one of the great paradoxes about allergy in that--and one sees this particularly in industrial situations where a person can be exposed to a material for years, have no rouble and then for some unknown reason, he will develop an allergy to this material. The converse is true, that allergies may go with continued exposure. For this one can think up some sort of plausible explanation, but why at any one moment of time a person will suddenly develop an allergy to a material to which he has been exposed for many years, I just do not know, but it does happen. DR. I. W. JAMIESON: What is your opinion of using panels of so-called dermatitis or eczema-prone subjects for testing cosmetics, in view of the difficulties of picking up sensitivity in normal populations? TIlE LECTURER: I think this is a bit immoral, and whether they are going to give you the right answer is another question. I think they may give you the answer as to what is going to happen in eczema-prone people when they are exposed to product X, but this is only a limited answer.

.[. Soc. Cosmetic Chemists 20 487-499 (1969) •_• 1969 Society o[' Cosmetic Chemists of Great Britaht Skin penetration C. W. BARRETT* Presented at the symposium on "Skin", organised by the Society of Cosmetic Chemists of Great Britain, at Eastbourne, Sussex, on 20th November 1968. Synopsis--The types of adverse reaction, both local and systemic due to penetration of the skin are summarised, and more recent views on pathways and mechanics of absorption discussed. Those factors influencing penetration are reviewed with particular reference to the physico-chemical properties of the penerrant, the vehicle, and the penerrant vehicle relation- ship. The usefulness of excised skin in diffusion cells as a method of determining penetration is described. INTRODUCTION Naturally occurring substances have been applied to the skin since the beginning of time, for belligerent and religious purposes as well as cosmetic and medicinal. That these substances might penetrate through the skin to produce serious toxic effects was not considered until the work of Schwenkenbecher in 1904 (1). He concluded from his experiments that the skin was permeable to lipid-soluble substances and gases, but practically impermeable to electrolytes and water. The rapid development of sensitive analytical techniques in the last 50 years has enabled research workers to monitor the passage of substances into, and through, the skin and learn something of the factors which either hinder or enhance their progress. Chemicals are being synthesised today in ever increasing numbers, for the dermatologist to treat skin conditions, for the cosmetic chemist to prepare a wider range of commercially available preparations and for an * The I,ondon Hospital, lx)ndon, E.1. 487