Sensitizer

In medical usage, a sensitizer is a substance that creates an allergic reaction in tissue or alters tissue to the point of making it susceptible to dermatitis or other allergic reaction. If something, a chemical or something natural, causes an allergic reaction in normal, healthy tissue in a high percentage of organisms it is considered a sensitizer. An example of this is the oil that is secreted by the poison ivy vine that causes a rash on exposed skin.