Pitfalls of irritant patch testing using different test chamber sizes.

BACKGROUND

Test chambers for irritant patch testing are usually larger than those used in allergic patch testing. In general, larger areas show stronger skin reactions than smaller areas.

OBJECTIVE

This study investigated whether this difference is of practical relevance, when a model irritant is applied in small and large Finn chambers and evaluated by measurement of transepidermal water loss (TEWL).

METHODS

Patch testing was performed with 2 concentrations of sodium lauryl sulfate (SLS) (0.25% and 0.5%) on forearms of healthy volunteers. Large (inner diameter, 12 mm) and small (inner diameter, 8 mm) chambers were used.

RESULTS

A variance analysis (3 factors, 2-tailed) showed that the test outcome, as assessed by TEWL, was strongly dependent on SLS test concentration and test chamber size. The larger chambers gave approximately 30% to 50% higher values than the smaller.

CONCLUSIONS

This may be explained by the fact that with the small chambers, the adjacent small area of nontreated skin was also assessed by the evaporimeter, biasing the results. A formula estimating TEWL value of the large chamber from values of the small chambers has been proposed.