due to personnel and financial restrictions, the study could not be conducted

Psoriasis and lichen planus often occur at mechanically irritated skin sites (e.g. tight clothing). The investigators would like to investigate this phenomenon in more detail in this study. For this purpose, the skin is specifically irritated at a small and cosmetically favorable site by tearing off scotch tape or rubbing with a wooden spatula. In order to be able to examine the inflammatory processes caused by the irritation more closely, a small skin sample and a skin swab are taken from the irritated area. This skin sample and the swab are repeated after three and fourteen days.

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.