Contact dermatitis (CD) is one of the most common inflammatory skin diseases. Distinguishing between allergic CD (ACD) and non-allergic forms, including irritant CD (ICD), remains challenging. Recent technological advances with the development of “omics” approaches allowed a better molecular characterization of these diseases, expanding our understanding of pathogenesis and the identification of skin biomarkers that could help to discriminate between both types of inflammation. These studies pave the way to the development of future diagnostic tools that could refine and simplify the management of CD patients.