Acne fulminans is a rare disease which typically manifests as an explosive worsening of acne lesions. The lesions are widely spread on the upper body and face. Acne fulminans can be associated with systemic symptoms. The article includes two case reports. The cause of AF in the first case was treatment with isotretinoin while in the second case no specific trigger was found. Such a classification is important because of different treatment strategies. A basic understanding of AF is essential considering that the patients might need hospitalization during the acute phase of the disease.