J. so½. Cosmetic Chemists 15 377-384 (1964) THE NEED FOR RABBIT SKIN STUDIES IN EVALUATING COSMETIC SAFETY I. LEVENSTEIN, Ph.D.* l•resented at the Symposium on "Toxicology of Cosmetic Materials", at Leamington, Warwicks., on 20th November 1963. The usefulness o• animal data in evaluating the safety o• cosmetic preparations is described. In •our examples cited the primary irritation in each o• three rabbits was confirmed by patch tests on twenty-five humans. The Food, Drug and Cosmetic Act under the jurisdiction of the U.S.A. Department of Health, Education and Welfare defines the term "Cosmetic" as (a) "Any article or articles intended to be rubbed, poured, sprinkled, or sprayed on, introduced into, or otherwise applied to the human body or any part thereof for the cleansing, beautifying, promoting attractive- ness, or altering the appearance", and (b) "any articles intended for use as a component of the aforementioned articles, except soap." Many new pro- ducts are compounded every year which fit this definition. Some contain old formulations and mixtures in new containers, but many incorporate new complex chemical materials which by virtue of some physiological activity, impart a beneficial change to the skin. These new materials may possess the ability to cause primary irritation, sensitization, systemic toxicity or blindness to the user. It is therefore necessary to evaluate the safety of each new preparation so that any toxic reactions may be discovered before the product is placed upon the market. The most reliable informa- tion, which would indicate the extent of toxicity of a product, can only be obtained from actual use in the human. Since, however, this type of experimentation may lead to dangerous consequences, a laboratory method must be developed which will give a measure of the risk associated with the use of a new preparation. It must be a reproducible procedure which can be relied upon to warn the cosmetic manufacturer of those materials which may be potentially dangerous if applied to the human. In investigating a new cosmetic for its safety, the oral toxicity, eye responses and skin reactions must be studied and evaluated. This paper is limited to those procedures which, we believe, are effective in determining the *Leberco Laboratories, Roselle Park, N.J., U.S.A. 6 377

378 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS safety of matehals following their application to the skin of laboratory animals. These are methods which research laboratories have employed for a long time, and which in the hands of experienced pharmacologists, have a high degree of reliability. They, therefore, can be used effectively to screen new chemicals and chemical mixtures. Our aim, in the laboratory, is to eliminate those preparations which may be irritating to the skin or, through absorption, show systemic toxicity. Using the animal as a substitute for the human, we use the same signposts as the dermatologist to judge effects. We look for reactions which may take the form, in order of severity, of primary irritation, sensitization or systemic toxicity. We have found that the response to a substance applied to the skin of the rabbit is reproducible, and often similar, to the response in the human. Potential hazards are evaluated by the use of laboratory animals which are raised under controlled conditions, and which react to the same irritants in a similar manner. Derreal changes in these animals, following application of an irritant, vary from slight erythema and edema to overt necrosis. These changes may be seen by gross observation or they may be magnified by histological section. Observations are made following single and repeated contact. A single application may cause no reaction while repeated applica- tions could result in skin responses which may or may not return to normal before each succeeding application. Some products are found which show reactions foilowing several applications. This response may disappear or become very mild after continuous treatment. As a result of many years of experience we have found that the rabbit, by virtue of its large skin area, ease of handling, maintenance and avail- ability, is the animal of choice for the screening of compounds. Although histologically the skin of the rabbit differs markedly from that of man in the relative thickness of the epidermal layer, and has a vigorous hair growth, we will attempt to show that results obtained from its use can be correlated with the responses which would occur in the human. The pig has been suggested as a better experimental animal, because of its lack of hair and thick epidermal skin layer, but its size makes it a difficult experimental subject. Sensitivity and general toxicity do not go hand in hand and are not interchangeable. Sensitivity is a random reaction and does not respond to a concentration gradient. An animal or human responds to a sensitizing agent if its threshold, which may be of a very low concentration, is reached. Sensitization in animals depends upon as many variables as sensitization in man. Factors of age, diet, previous or present illness, environmental conditions, sex and method of application all play a part. Animal experience indicates that strong sensitizers may be picked up in the guinea pig and