Weak Patch Test Reactions at 48 Hours Can Provide an Understanding of a Work-Related Dermatitis: A Study of Epidemic Hand Dermatitis in Industrial Clay Modellers

We examined a 2-year hand dermatitis epidemic among 142 industrial clay modellers who were using wood rosin-containing clay. We questioned, examined, and patch test screened 25 modellers at 48 hours. Ten were examined at 96 hours also. Most normal controls had some patch test reaction to the clay at 48 hours, in 40% this was still evident at 96 hours. Twelve of the 25 modellers (48%) fulfilled criteria for probable workrelated dermatitis even with patch testing criteria excluded. Substitution of a petroleum resin for wood rosin in the clay reduced symptomatic skin pathology. Both 48- and 96-hour weak 1 + -3+ patch test reactivity to work-related allergens indicated a clinically diagnosed probable work-related dermatitis with greater sensitivity yet with equivalent or only slightly less specificity than 1 + -3+ reactivity. Moreover, statistically significant correlation existed between clinically diagnosed probable work-related dermatitis and both 48-hour weak 1 + -3+ clay and 48-hour clay component reactivity, which was greater than the correlation between such dermatitis and 48 hour 1 + -3+ reactivity alone. The explanation is that the clay is an irritant and trapped under fingernails. Because of this, a closed patch test result would more likely mimic real life exposure conditions.