Allergic contact dermatitis resulting from exposure to a chemical or chemicals is a common diagnosis in the dermatologist's office. We are exposed to hundreds of potential allergens daily. Patch testing is the criterion standard for diagnosing the causative allergens responsible for allergic contact dermatitis. Patch testing beyond standard trays is often needed to fully diagnose patients, but not all dermatology practices have access to this testing procedure or these allergens. In order to adequately evaluate patients, physicians must understand the pathophysiology of the disease process and be well versed in the proper evaluation of patients, indications for patch testing, proper testing procedure, and other diagnostic tools available and be aware of new and emerging allergens.