Eczema vaccinatum is a rare and serious complication that can occur after smallpox vaccination. Some synonyms for this condition include vaccinia eczema, eczema varicelliforme, and progressive vaccinia. It is characterized by a widespread rash that typically begins on the site of the vaccination and then spreads to other parts of the body. It can be especially dangerous for individuals with preexisting eczema or other skin conditions. Symptoms can range from mild to severe and can include fever, fatigue, and swollen lymph nodes. Treatment options include antiviral medication and supportive care, but prevention through avoiding smallpox vaccination in at-risk individuals is the most effective method.