Allergic contact dermatitis commonly known as skin sensitization affects 15-20% of the general population. According to the adverse outcome pathway, following the exposure of a sensitizing compound to the skin, proteins are covalently modified by the sensitizer. The haptenated proteins are degraded and the peptide-hapten adducts are presented as antigens. Hence, the subsequent exposure with the same sensitizer results in epidermal inflammation. There is an urgent industry need for in vitro methods to access the sensitizing potential of chemical compounds. In the study, we employ high resolution mass spectrometry combined with cellular thermal shift assay (CETSA-MS) as well as product ion monitoring method to discover proteins targets involved in haptenation using a set of chemicals with known sensitizing potentials. Using CETSA-MS, we have identified a list of proteins that are commonly targeted by extreme sensitizers. In complement to our CETSA-MS approach, we develop the product ion monitoring method for identifying the peptide-adducts in peptide mixtures. These MS based methods provide novel in vitro approaches to determine the sensitizing potential of unknown chemical compounds as well as to gain insights into pathways involved in allergic contact dermatitis.