Abstract: Allergic contact dermatitis (ACD) is a common T cell-mediated type IV allergic reaction, which is mainly divided into three stages: sensitizing phase, irritating phase and regression phase. The cellular and molecular effects involved in each stage are different，which may become a new target for the treatment of ACD. The update of immunological mechanism of allergic contact dermatitis is reviewed in this paper.

Key words: contact dermatitis, hapten pattern, recognition receptor, dendritic cells, T lymphocytes