In the present study we have shown that hydrophilic ointment and a similar vehicle containing 1% sodium lauryl sulfate invariably produce contact irritant dermatitis when they are occluded 16 hours a day for more than three days. Sodium lauryl sulfate is the provocative agent. Previous experimental work on sodium lauryl sulfate suggests that denaturation of epidermal proteins and subsequent loss of the epidermal barrier are the likely mechanisms. Less irritating emulsifiers, or concentrations of sodium lauryl sulfate less than 1%, should be used in topical products, especially those that might be used under occlusion.