Patch testing with mineral wool (Rockwool).

25% of 315 tested subjects exhibited skin reactions when patch tested with mineral wool. Coating of the mineral fibres with phenol-formaldehyde did not influence the skin reactions. The reactions seem to be induced mechanically, as the mineral without the fibres did not give any reactions. No allergic reactions to the chemical additives were demonstrated. Macroscopically, the reactions may simulate an allergic response; microscopically, they seem to be toxic, sometimes with prominent spongiosis.