The epidemiology of occupational contact dermatitis

Occupational contact dermatitis (OCD) ranks first of all occupational diseases in many countries. The incidence rate is believed to be around 0.5–1.9 cases per 1000 full-time workers per year. Epidemiological studies play an important role in observing disease trends, analysing risk factors, and monitoring the effect of preventive measures. In this review article the lack of truly epidemiologic data on OCD and the difficulties of those studies are illustrated. The following issues are highlighted: case ascertainment and bias, the distribution of allergic and irritant contact dermatitis in the working population, the interrelationship between exogenous (allergens, irritants) and endogenous factors, the prognosis, the social and economic impact, and the need for intervention studies. Received: 26 January 1999 / Accepted: 24 April 1999     

Penetration and haptenation of p‐phenylenediamine

Although p‐phenylenediamine (PPD) has been recognized as an extreme sensitizer for many years, the exact mechanism of sensitization has not been elucidated yet. Penetration and the ability to bind to proteins are the first two hurdles that an allergen has to overcome to be able to sensitize. This review is an overview of studies regarding PPD penetration through skin (analogues) and studies on the amino acids that are targeted by PPD. To complete this review, the auto‐oxidation and N‐acetylation steps involved in PPD metabolism are described. In summary, under normal hair dyeing exposure conditions, <1% of the applied PPD dose penetrates the skin. The majority (>80%) of PPD that penetrates will be converted into the detoxification products monoacetyl‐PPD and diacetyl‐PPD by the N‐acetyltransferase enzymes. The small amount of PPD that does not become N‐acetylated is susceptible to auto‐oxidation reactions, yielding protein‐reactive PPD derivatives. These derivatives may bind to specific amino acids, and some of the formed adducts might be the complexes responsible for sensitization. However, true in vivo evidence is lacking, and further research to unravel the definite mechanism of sensitization is needed.     

Sensitivity,specificity and positive predictivevalue of patch testing: the more you test,the more you get?

Pathophysiological variability affects the results of patch testing. In addition, even a minimal degree of test-imprecision due to this variability has a number of important statistical consequences for the analysis and interpretation of any patch test data set. One such statistical phenomenon that is often overlooked is the dependence of the positive predictive value (i.e., the predictive value of a positive patch test) on sensitivity and specificity, the impact of which is heavily dependent on the proportion of truly allergic subjects that are studied. A 2nd important issue is the fact that patch testing is performed in series, which means multiple tests. If we assume, for example, a patch test series of only 10 allergens, then it can be demonstrated that there is a random probability of over 40%) to find, simply by chance, for at least 1 allergen, a statistically significant difference between 2 groups of patients. Comparison of the results of series between patients calls for statistical adjustments in order to prevent erroneously positive differences and/or associations.     

Susceptibility to primary irritants

Patch tests with three primary irritants were performed in 600 persons with eczema and in 33 healthy controls, The irritants assayed were: croton oil (20%) in mineral oil, thymoquinone (1%) in ethanol and crotonaldehyde (7.5%) plus sodium lauryl sulphate (4%) in aqua dest. The number of positive reactions to croton oil was found to decrease with age, while for thymoquinone and crotonaldehyde and for the total irritant score no age dependence was observed. No significant correlation was found between sensitization to common contact allergens and susceptibility to irritants. The incidence of positive reactions to common allergens proved to increase with age.     

Effect of mineral oil and linoleic-acid-containing emulsions on the skin vapour loss of sodium-lauryl-sulphate-induced irritant skin reactions

This study evaluates the influence of mineral oil and linoleic-acid-containing emulsions on the skin vapour loss (SVL) of detergent-induced irritant skin reactions. During a period of 2 weeks, 2 x 45 min applications of a sodium lauryl sulphate solution of low molarity were performed on the forearm of 9 volunteers. In the same period, a standard amount of each emulsion was applied on the induced irritant skin reactions, 3 times each day. The effect of the emulsions on the barrier function of the skin was evaluated by means of SVL measurements. The emulsion based on mineral greases significantly reduced SVL values during both weeks, possibly because of an occlusive effect. The emulsion with 15% of linoleic acid significantly reduced SVL values during the 1st week but not during the 2nd week. The emulsion with 38% of linoleic acid did not reduce SVL values at all.