Diphenylmethane diisocyanate (MDI) is widely used in its polymeric form in the manufacturing of polyurethane products. Previous reports on MDI-related contact allergy have shown a pattern, where patients seem to react to their own MDI-based work material but not to commercial patch-test preparations, which contain 4,4'-MDI. Therefore, we performed chemical analyses of 14 commercial test preparations of 4,4'-MDI obtained from 8 European and 4 American dermatology departments as well as 2 preparations from 2 major European suppliers of patch-test allergens. A new method for monitoring 4,4'-MDI in petrolatum preparations was developed and the determination of 4,4'-MDI as the MDI-dibutylamine derivative using liquid chromatography-mass spectrometry was performed. None of the preparations obtained from the dermatology departments contained more than 12% of the concentration stated on the label. In most cases, 4,4'-MDI content was only a few percentages or less of the concentration stated. 7 of the 14 preparations were analysed before the expiry date. Yet, only 1 of them, a preparation directly obtained from the supplier, came close to the concentration stated on the label. Thus, using these preparations, patients will be tested with a lower concentration than intended, leading to possible false-negative reactions.

Over a short period of time, there was an outbreak of work-related skin lesions among workers at a company producing flooring laminate boards, after the introduction of a water-repellent lacquer based on diphenylmethane-4,4'-diisocyanate (MDI). In 5 workers, patch testing was performed with a standard series, an isocyanate series and work-environmental products when indicated. 3 of the workers were tested with the lacquer, and contact allergy was found with concurrent reactions to 4,4'-diaminodiphenylmethane (MDA). 1 of the 3 workers also showed a simultaneous reaction to MDI, whereas 1 showed a positive reaction to dicyclohexylmethane-4,4'-diisocyanate (HMDI). Of the 2 individuals not tested with the lacquer, 1 reacted to both MDI and MDA, whereas the other reacted to a soap used at work. In 3 of 4 cases, the isocyanate reactions appeared after D3. Occupational contact with isocyanates should not exclusively be focused upon respiratory hazards, as this report shows that skin contamination probably increases the risk of developing contact allergy to isocyanates and isocyanate-related substances. When aiming at diagnosing contact allergy to isocyanates, it is desirable to perform a late reading, as positive reactions appear late. MDA appears to be a good marker for isocyanate hypersensitivity.

In a plant producing advanced components for engines and drivelines we undertook a survey of occupational dermatoses, based on a questionnaire, clinical examination, and patch testing with a standard series and a series of samples from the working environment. The questionnaire was given to all 430 employees and it was answered and returned by 382 of these. 214 reported having had or having skin manifestations during the time of employment suspected of being work-related. 183 employees (164 metal workers, 19 office staff) participated in the clinical investigation, 182 (163 metal workers, 19 office staff) being patch tested. Occupational dermatoses were diagnosed in 23 of these 163 (14.1%) and in 1 of these 19 (5.3%). In all, irritant contact dermatitis was diagnosed in 12 metal workers, occupational allergic contact dermatitis in 11 (10 metal workers and 1 office clerk) and folliculitis in 1 metal worker. In the 11, neat oils were the cause in 4 workers, a water-based cutting fluid in 3 and various biocides in 4.

From August 1999 to April 2001, there was an outbreak of severe eczema at a factory manufacturing medical equipment. A glue, mainly based on the isocyanate dicyclohexylmethane-4,4'-diisocyanate (DMDI), was suspected as being the cause of the problem. 16 workers with recent episodes of eczema were patch tested with a standard series, an isocyanate series and work material. The latter consisted of, among other things, the glue, DMDI, and an amine, dicyclohexylmethane-4,4'-diamine (DMDA), which is formed when DMDI reacts with water. 13 patients reacted to DMDI, 9 to 1,6-hexamethylenediisocyanate (HDI) and 4 to isophoronediisocyanate (IPDI), all of which are aliphatic isocyanates. None reacted to the aromatic isocyanates, diphenylmethane-4,4'-diisocyanate (MDI) or toluenediisocyanate (TDI). One explanation for this pattern could be that aromatic diisocyanates are more reactive than the aliphatic ones and that, therefore, they are inactivated before penetrating the skin. 5 patients reacted to DMDA and 5 to 4,4'-diaminodiphenylmethane (MDA). Concurrent reactions to DMDA and or MDA with DMDI could be due to cross-reactivity. The positive reactions to MDA could also be a marker of MDI exposure. Yet another patient, investigated in 1997 with suspected work-related contact dermatitis from the glue, is described. She, however, showed no positive reactions to any isocyanates.

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