TESTING DRUGS FOR DERMAL TOXICITY 389 of the general health of the animal, and the blood and urine are tested from time to time. At the end of the experiment the animals are killed and the main organs and tissues examined histopathologically. Finally, whenever a substance is applied to the skin for a prolonged period of time a danger of carcinogenicity must be considered. An indication of this may be obtained in the chronic toxicity studies, but it is better to set up specific tests. Since most strains of animals have a natural incidence of turnours, it is essential to include an adequate number of controls. Treated and control groups should be of equal size, and should include an equal number of males and females. •ice and rabbits are most frequently used, rats being unsuitable. The test and control groups should contain at least 50 mice and 10 rabbits. The compound, or formulated preparation, should be applied to the same area of skin twice weekly for one year, after which they are observed for a second year. In mice the dorsal skin is used, and in rabbits the dorsal skin or ears. The animals are observed weekly, and the incidence and time of appearance of turnours is recorded in the test and control groups. A full histopathological examination is made of any animals affected during the test, and of all the animals at the end of the experiment. (Received: 8th October 1965.) REFERENCES (1) J. H. Draize Appraisal of the Safety of Chemicals in Foods, Drugs and Cosmetics 46 (1959) (Association of Food and Drug Officials of the U.S.A.). (2) J. W. Hadgraft and G. F. Somers J. Pharm. and Pharmacol. 8 625 (1956). Introduction by the lecturer My paper briefly reviews the main types of tests to which a substance should be subjected for the detection of toxic effects when applied to the skin. It rightly points out that these tests cannot give complete assurance that the substance may be entirely safe. A very real problem, which we have, is our inability to detect sensitizing substances in animal studies. We are concerned with a number of testing procedures firstly local toxicity, that is the local effects when the substance is applied to the skin acute effects refer to single applications, chronic effects to repeated applications. The animal which is used is usually the rabbit and it is interesting to observe that Dr. Levenstein* and I are in a measure of agreement with regard to the use of the pig which has, we recognize, a suitable skin but an unsuitable size. It is my intention, in this brief survey, to bring to your notice various problems which occur in testing for local irritant properties in the rabbit. Certain factors have to be considered firstly we have the prepara- tion of the skin--should it just be clipped, or should we use a chemical * I. Levenstein J. soc. Cosmetic Chemists 15 011 (1964)

390 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS depilatory ? Secondly, we have the question of whether or not the skin should be covered during part of the test or throughout the period of observa- tion. Thirdly, how should we score the effects so that we can make relative comparisons between different substances ? Lastly, we may need to discuss the need or value of scarifying the skin before applying the test material. Many of us use the rabbit test and in the pharmaceutical industry we arranged a collaborative trial between a number of companies. The results were remarkably in agreement--that is to say we all successfully placed three substances in order of irritant properties, but what we are not so clear about is the ultimate meanings of these tests when applied to man. We certainly know that if nitric acid is put on the skin of a rabbit and burns a hole in it, we may expect the same effect in man! But when a substance in a rabbit produces a certain amount of erythema, will this apply in man ? There are numerous examples where one gets opposed answers between man and rabbit. Another technique that we have used successfully for testing skin toxicity is to inject the material intradermally into the skin of the guineapig. One observes the reactions which occur after a period of a few hours, and subse- quently over a period of 7 days. By a system of standard reference pictures, which were supplied by Dr. Paget of I.C.I., we are able to grade the severity of the reaction on a scoring system. Such a test is intermediate in sensitivity between the rabbit skin test and the rabbit eye test, and I personally like it because it does have some humane value in preventing us putting in the eye of a rabbit something which obviously is going to cause a great deal of damage. In the rabbit eye test, the test substance is applied, usually in solution, into the eye and the subsequent reaction which occurs is observed. Again there are a variety of disciplines. Some people follow the original method of Draize, instil the solution into the eye and simply wash it out again within a few seconds. Others leave the solution in the eye and observe the effects which occur. The question arises how often one should look at the eye--at hourly intervals ? Overnight ? And so forth. Lastly, a few words about sensitization studies. I do not think any of us in this country would regard an animal test for sensitivity to be of any real value. Methods have been described where the material is injected into the skin of the guineapig over a period of time, and then subsequently re-tested about a fortnight after. These tests may detect the more potent sensitizers but we are more concerned with those peculiar in man. These require human patch tests. In addition to the local toxicity tests of a compound when applied to the skin, we have to consider the systemic effects which follow after absorption of toxic substances through the skin. These occur as distant toxic effects.