The tendency for skin lesions to appear on lines of trauma. Conditions demonstrating linear lesions after a linear exposure to a causative agent include: molluscum contagiosum, warts and toxicodendron dermatitis (a dermatitis caused by a genus of plants including poison ivy). Warts and molluscum contagiosum lesions can be spread in linear patterns by self-scratching ("auto-inoculation").

Koebner is best known for his work in mycology. His intense nature is illustrated by the following: in a medical meeting, he proudly exhibited on his arms and chest three different fungus infections, which he had self-inoculated, in order to prove the infectiousness of the organisms he was studying. The Koebner phenomenon is the generalized term applied to his discovery that on psoriasis patients, new lesions often appear along lines of trauma.