Interlaboratory studies with a proposed patch test design to evaluate the irritation potential of surfactants.

Background: Development of cosmetic products and household detergents necessitates comparative study designs to assess the skin tolerance of products. In initial tests, the epicutaneous patch test for irritation is widely used.

Objectives: This study was conducted to develop a protocol that would facilitate a comparison of results obtained when tests are conducted by different laboratories.

Methods: 'In-house' and standardized patch test protocols were used to assess irritation potentials of surfactant-based products in intra- and interlaboratory studies using defined surfactant samples.

Results: The various in-house protocols tested did not consistently produce equivalent results. In order to develop a study design that yields comparable results, various factors were identified and adjusted. The standardized study protocol includes occlusive application of 70 microl of the test substance to the back of 30 subjects, defined reading times and schemes, assessments based mainly on erythema, and inclusion of sodium laureth sulfate and sodium dodecyl sulfate as positive controls as well as water as a negative control.

Conclusions: Use of the standardized protocol and training of assessors improved the reliability and consistency of results whereby the irritation potentials of the references and test samples were ranked similarly by the laboratories.