Allergic contact dermatitis (ACD), like most allergic responses, develops in two phases and is dependent on the induction of an immune response. The first phase, often called the induction phase or sensitization phase, is initiated when skin is exposed to a hapten, that is sufficient to trigger an immune response resulting in the priming of specific immune cells. This phase typically has no clinical symptoms. An individual that has acquired skin sensitization through the priming of these cells, now has the ability to launch a more aggressive response upon re-exposure of the product at the same or even a distant skin location. This second phase is referred to as the elicitation phase and is characterized as allergic contact dermatitis.
Allergic contact dermatitis is not life threatening, however it is long-lasting. Therefore, there is a continuing need for accurate identification and characterization of products that have the potential to cause skin sensitization. A product or substance is classified as a skin sensitizer when data shows that it can produce a sensitization response "in a substantial number of persons" or when "there are positive results from an appropriate animal test." (UNECE, 2004, p. 152).
Skin sensitization has in the past been determined using animal models and has been well-served in these methods. However, there is now significant interest in new approaches that will reduce the need for animal testing or replace animals altogether. This in vitro dermal sensitization model provides a useful tool for identifying products as skin sensitizers without the use of animals.