Contact hypersensitivity is a type IV hypersensitivity reaction that affects about 20 % of the population around the world. It is triggered by a group of chemically-reactive, small molecular-weight compounds called contact allergens. Despite the known dangers of contact allergens and the increase in the number of patients, the pathology at which contact dermatitis develops remains unclear. This dissertation aims to understand a molecular mechanism of contact dermatitis by investigating contact allergen’s interaction with protein targets. Chapter 2 reports a structure-activity relationship of a model contact allergen, 1-chloro-2,4-dinitrobenzene (DNCB). The overall sensitization potential of DNCB and its derivatives, chosen based on DNCB’s reaction mechanism, were evaluated by different types of assays that can encompass both physicochemical and biological properties. Peptide reactivity and immune cell-based assays revealed a non-linear correlation that requires a balance of stability and reactivity that dictates a contact allergen’s ability to induce the sensitization phase. This also indicates that a non-allergenic compounds can be made to cause sensitization by controlling their rate of reactivity. In chapter 3, this dissertation shows the identity of protein targets that DNCB reacts to bind during the sensitization phase. Starting with an unbiased sampling, mass spectrometry analysis revealed 9 DNCB-modified proteins. To elucidate the function of the proteins in contact hypersensitivity, cells carrying suppression of the DNCB-modified proteins were cultured with DNCB to evaluate their DNCB-induced response. Real-time PCR revealed that HSP90-knockdown cells reduced DNCB-induced hypersensitivity below the background levels. DNCB’s activity was attenuated when it was cultured with geldanamycin, a known inhibitor of HSP90, or anti-CD91, an inhibitor for HSP90 receptor, all of which validate observations from qPCR. As heat shock proteins are stress-responsive proteins and the molecular chaperones in antigen processing, it is possible that they are the first proteins to respond to DNCB stimulation and the modification somehow signals the activation of the immune cells. These results, altogether, are one of the first evidence and validation of HSP90’s involvement in DNCB-induced hypersensitivity and report that the degree of hypersensitivity can be reduced by inhibiting HSP90.