Contact allergy to colour developing agents in the guinea pig

Skin sensitisation, vehicle effects and the local lymph node assay

Accurate risk assessment in allergic contact dermatitis is dependent on the successful prospective identification of chemicals which possess the ability to behave as skin sensitisers, followed by appropriate measurement of the relative ability to cause sensitisation; their potency. Tools for hazard identification have been available for many years; more recently, a novel approach to the quantitative assessment of potency--the derivation of EC3 values in the local lymph node assay (LLNA)--has been described. It must be recognised, however, that these evaluations of chemical sensitisers also may be affected by the vehicle matrix in which skin exposure occurs. In this article, our knowledge of this area is reviewed and potential mechanisms through which vehicle effects may occur are detailed. Using the LLNA as an example, it is demonstrated that the vehicle may have little impact on the accuracy of basic hazard identification; the data also therefore support the view that testing ingredients in specific product formulations is not warranted for hazard identification purposes. However, the effect on potency estimations is of greater significance. Although not all chemical allergens are affected similarly, for certain substances a greater than 10-fold vehicle-dependent change in potency is observed. Such data are vital for accurate risk assessment. Unfortunately, it does not at present appear possible to predict notionally the effect of the vehicle matrix on skin sensitising potency without recourse to direct testing, for example by estimation of LLNA EC3 data, which provides a valuable tool for this purpose.

Concomitant contact dermatitis due to textile dyes and to colour film developers can be explained by the formation of the same hapten

p-phenylenediamine derivatives are widely used in industry and in cosmetics, and several of them are well-known sensitizers. One group of allergenic p-phenylenediamine derivatives are used as colour film developers. Cross-reactivity between the colour film developers has been reported. In this paper, an occupational facial dermatitis due to colour film developers is described. The patient reacted to colour film developers (CD-1, CD-2, CD-3, and CD-4), but not to other p-phenylenediamine derivatives tested. He also showed allergic reactions to Disperse Blue 106 and Disperse Blue 124 and to Disperse Red 17, but not to Disperse Orange 3. The activation of the colour film developers by oxidation at physiological pH was analysed with chemical methods, and the mechanism responsible for the concomitant reactivities to the colour film developers and the disperse dyes at a molecular level is discussed.

Further investigation of the prohapten concept: reactions to benzene derivatives in man

p-Phenylenediamine (PPDA) is a strong contact sensitizer which is included in the standard patch test tray and which can also act as an indicator of allergy to related substances by virtue of cross-reactions. In a previous study, the pattern of cross-reactions between PPDA and related substances was investigated in the guinea pig to evaluate the prohapten concept. The results provided some support for this concept, but also indicated that a number of reactive intermediates might be behaving as haptens. This work has now been extended to an examination of the prohapten concept in man in PPDA-allergic subjects. These subjects were tested with 7 substituted benzenes, plus PPDA. Of these, the 1,4-substituted benzenes hydroquinone, Metol, PPDA and p-aminophenol are all capable theoretically of giving rise to benzoquinone by oxidation (after demethylation in the case of Metol). However, as had been the case in the guinea pig, only a limited degree of cross-reaction was observed. Only one of the subjects allergic to PPDA gave a clearly positive allergic reaction to benzoquinone. The data provided only limited support for the prohapten concept in terms of benzoquinone as the ultimate hapten for a range of 1,4-substituted benzenes. As indicated in the guinea pig, a range of reaction intermediates or indeed other oxidation products may be involved. So, for each molecule, the sensitizing activity and potential to give rise to cross-reactions may depend on the balance between routes of skin metabolism.

Occupational dermatoses at a film laboratory. Follow-up after modernization

The occurrence and causes of occupational dermatoses at a film laboratory following modernization was studied. In 1983 the film laboratory moved to new premises built to reduce exposure to hazardous chemicals. The study was carried out during 1983-1986 with repeated interviews and dermatological examinations of all employees (78 subjects) and patch testing those with a history of or with current chemical exposure or dermatitis (65 subjects). Of 54 chemically exposed subjects, 34 (63%) had a history of occupational dermatoses, and 12 (22%) were contact allergic to film chemicals. Current, probable occupational dermatoses were observed in 13 subjects--thereof 8 with hand eczema. No new case of occupational skin disease occurred during the investigation period, except for 1 case of ulceration from an acid splash. Petrolatum mixtures of the colour developing agents, Metol and hydroquinone were found most suitable for patch testing, since these chemicals are unstable and/or cause irritation in aqueous solutions. It is concluded that occurrence and severity of occupational dermatoses had been reduced by the technical measures taken to reduce chemical exposure.