Development of a sensitive test method to evaluate mechanical irritation potential on mucosal skin
Authors: Farage Miranda A. , Meyer Sandy , Walter David 
Published: April 2004

Background/purpose: The studies presented here are intended to continue the validation of the behind‐the‐knee test system developed to evaluate the mechanical irritation potential of products such as catemenial pads, baby and adult diapers (which are inherently non‐irritating products/chemicals). These products are intended to be worn for prolonged periods of time on body sites that include the mucous membrane and non‐keratinized epithelium in addition to normal squamous cell epithelium. These studies had two specific goals. The first was to validate the test model using a variety of conditions, including those that mimic the conditions that exist during normal product use. The second specific goal was to determine the most cost‐effective protocol to use for screening different product executions for potential irritant effects. If the model proves to be reliable under a variety of conditions, it will be an ideal test system to use in claims support studies, where it is preferable to mimic use conditions as closely as possible. We were also interested in evaluating sensory responses that consumers often associate with irritation to determine if any of these sensations correlated with objective measures of irritation.

Methods: Three test materials were used in these experiments. All three are commercially available catemenial pads that were expected to be similar, but not identical, in irritant properties based on subjective consumer reports of irritation associated with product use. Test materials were applied daily to the area behind the knee and held in place for 6 h by an elastic knee band of appropriate size. Irritation was graded 30–60 min after test product removal, and the following morning before application of the next sample. Two products were compared using four different protocol variations: dry product on intact skin, dry product on tape stripped (compromised) skin, wet product (i.e., product loaded with 8 mL of saline) on intact skin and wet product on compromised skin. An additional study compared the two products using two protocol variations (intact skin/dry product vs. compromised skin/wet product). In addition, a study (#5) was conducted to compare a third product applied wet on intact vs. compromised skin. In the final two studies, information was collected from the panelists on subjective sensations of irritation.

Results: All four protocol variations were capable of detecting significant differences between the products. These differences were directionally similar to what was expected based on subjective consumer comments. In addition, a higher number of certain perceived sensory effects were reported for the more irritating product.

Conclusions: In these studies, Product A is more irritating than Product B when assessed objectively, i.e., by scoring irritation at the test sites, and subjectively, i.e., by evaluating reports of adverse sensations perceived by panelists. There is no clear relationship between specific test conditions, i.e., compromised skin and/or testing wet samples, and reports of perceived sensory reactions. However, some sensory reactions appear to be associated with higher levels of irritation. The most cost‐effective protocol to use for screening for potential irritant effects for catemenial pads, baby and adult diapers is two 6‐h sample applications on intact skin, with scoring in the afternoon 30 min after removal of the sample. For claims support testing, a variety of test conditions can be used in the behind‐the‐knee assay to mimic the exposure conditions for the product under evaluation, including using compromised (tape stripped) skin and wet product samples.