Histological differences between irritant and allergic patch test reactions in man

The results of a study of the histological aspects of the application of DNCB on the skin of unsensitized and sensitized persons are discussed. The nature of the histological changes in primary irritant and allergic reactions to DNCB in human skin appeared to be identical. The differences appeared to be primarily of a quantitative character. It is furthermore concluded from data in the literature that the skin of some persons may react with a primary irritant reaction to concentrations of a compound thought to cause only allergic reactions. In these persons histological examination of the patch test result may give insufficient clues as to the nature of the reaction. The practical consequences of the data presented are discussed.