SINCE the introduction of cold-wave preparations for home use in 1945, consumer usage has increased year by year, reaching a figure of some 37 million in 1949. As the agents used in the cold-wave process contact hair and skin, the subject becomes of direct interest to dermatologists. The purpose of this report is to examine the basic theoretical principles, materials, and techniques employed in the cold-wave process, primarily to clarify the mechanisms through which reactions of medical or medicolegal importance may develop. Figures obtained from the files of a manufacturer of home cold-wave products have been used to evaluate the frequency of these reactions. Previous reports have, in general, cited only isolated case histories of patients with some dermatologic or systemic manifestation allegedly associated with the use of cold-wave preparations, so that it has been difficult to obtain a clear concept of the causes, characteristic features, or frequency