During contact us small molecule from the planned called a hapten blinds to a carrier protein in the host. The carrier protein with bound hapten is ingested by macrophage and the hampton peptide present on the surface of the macrophage
On a class to MHC th1 cell with T cell receptors capable of recognizing hapten peptide antigen interact with the presented antigen become activated increase in numbers. When the host comes in contact with the allergen a second time the th1 cell react with the Hampton peptide being presented on the macrophage and release 80 kind resulting in attraction of more macrophages followed by inflammation and skin lesions characteristic skin reson appear after 24 hours reaching their peak and 48-72 hours after the second exposure to the plant