In selecting a new material for human contact in medical applications, it is important to ensure that the material will not stimulate the immune system to produce an allergic reaction. The reaction would be due to substances which could leach out of a material. Therefore, this practice provides for using material extracts. The rationale for this practice is based on the fact that the guinea pig has been shown to be the best animal model for human allergic contact dermatitis. The use of Freund'complete adjuvant and sodium lauryl sulfate tends to enhance the potential of a material to cause an allergy. Therefore, this test, while not guaranteeing that a material is nonallergenic, is the most severe animal test in common use today.