Development of a new test for mechanical irritation: behind the knee as a test site

Certain consumer products, such as feminine hygiene products, and baby and adult diapers, are worn for prolonged periods of time in close proximity to the skin. A sensitive test method was needed to evaluate these products and their components for the potential to cause mechanical irritation during use.

We investigated several test sites on the body where normal, daily activities provided the opportunity for movement and, therefore, friction. These test sites were: the back of the knee, the axilla, and the wrist. Three exposure regimens were tested: 6-h daily for 4 days, 24-h daily for 3 days, and 24-h daily for 4 days. Controls consisted of satin fabric (a non-irritating material) or burlap (an irritating material). Test materials were secured to the test sites using an Ace elastic bandage (on the back of the knee), a snug fitting garment (on the axilla), or an athletic band (on the wrist). Test sites were scored for irritation on a visual scale prior to the initial application and 30-60 min after removal each day. Data were evaluated for the ability to reliably detect irritating materials, and for the ability to consistently differentiate between irritating and non-irritating materials. Quantitative measures of these abilities were used to rank the overall effectiveness of various test protocols as a model for mechanical irritation.

The results of these studies indicated that a protocol using the back of the knee as a test site with an exposure regimen of 6-h daily for 4 days, best met the success criteria for an effective test system for evaluating mechanical irritation.