Drug reaction with eosinophilia and systemic symptoms (DRESS) is a rare, potentially life-threatening reaction to certain medications. It is characterized by a combination of skin rash, fever, lymphadenopathy (swollen lymph nodes), and an abnormally high number of eosinophils (a type of white blood cell) in the blood. The exact cause of DRESS is unknown, but it is thought to be an immune-mediated reaction to certain medications. Commonly implicated medications include anticonvulsants, sulfonamides, allopurinol, and minocycline. Other potential causes include infections, such as herpes simplex virus, and certain types of cancer.