Koebner's Phenomenon in Psoriasis and Lichen Planus

Inclusion Criteria: * Dermatologist diagnosed psoriasis (group psoriasis), lichen planus (group lichen planus) or no skin disease (group healthy controls) * Subject is capable of giving informed consent * Signed informed consent Exclusion Criteria: * Use of systemic immunosuppressive/immunmodulating agents in the last three months * Use of topical anti-inflammatory treatment in the last 7 days in the area of sampling. * Phototherapy in the last 4 weeks * Active or recurrent serious bacterial, fungal or viral infection at the time of enrollment by patient history, including patients with Human Immunodeficiency Virus (HIV) infection, Hepatitis B and Hepatitis C infection, active or untreated latent tuberculosis. * Female patients of childbearing potential who are pregnant or breast feeding or planning a pregnancy during the duration of the trial and/or not practicing acceptable birth control for the duration of the trial * Known or suspected non-compliance, drug or alcohol abuse, * Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc. of the participant, * Previous enrolment into the current study, * Enrolment of the investigator, his/her family members, employees and other dependent persons.