For nearly twenty years, Dr. Krengel has focused on experimental and clinical research on pigmentary cell function and pigmentary disorders. In 2005, he initiated naevus-netzwerk.de, which became Nävus-Netzwerk Deutschland, in order to enable self-help and support of nevus patients and parents from German-speaking countries. In collaboration with Drs. Marghoob, Scope and Dusza, he spearheaded a new consensus classification for congenital melanocytic nevi (Journal of the American Academy of Dermatology, 2013).

Dermatological group practice (Dermatologische Gemeinschaftspraxis), Lübeck, Germany