Epidermal rupture is the initiating factor for the Koebner response in psoriasis.

The Koebner phenomenon was studied using low pressure suction and/or sellotape stripping. Each of 10 patients with psoriasis had 5 suction blisters induced and sellotape stripping. In each patient the roof of 4 of the 5 blisters was removed. In 6 of the 10 patients, psoriasis developed where the blister roof was removed, but not where the blister was left intact. However, only 3 of these 10 patients were also Koebner-positive at the tape-stripped site. Similarly, in a group of 37 psoriasis patients who were sellotape-stripped alone, only 8 (21.6%) were Koebner-positive at the tape-stripped site. In another experiment, 5 suction blisters were produced in each of 4 patients. The roof of 4 blisters was removed, one of which was occluded. Psoriasis developed in 3 of the 4 patients, but only where the blister roof had been removed and left unoccluded. These findings suggest that rupture of the epidermis can initiate the Koebner response, but that secondary dermal events are necessary for a psoriatic lesion to form.