∙ Patients:

⁃ Able to understand and provide a written informed consent prior to any study procedures

⁃ Male or non-pregnant female, ≥18 years of age

⁃ Patient is willing to refrain from extensively washing (including bathing, swimming) the target lesional skin 12 hours before every study visit day.

⁃ Patient is willing and able to comply with the study protocol

⁃ Female participants are willing to not get pregnant between M0 until M12, from study entry to the last study visit

⁃ The patient is willing to start the prescribed treatment.

∙ Disease-specific inclusion criteria

∙ For patients with AD:

∙ To be eligible to participate in this study, a subject must meet all of the following criteria:

∙ 6\. Diagnosis and history of chronic, moderate-to-severe AD (by the Eichenfield revised criteria of Hanifin and Rajka for at least 3 years before baseline visit.

∙ 7\. Documented recent history (last 6 months) of eligibility for (local or systemic) treatment with immunosuppressants, biologics or JAK-inhibitors.

∙ 8\. When applicable, documented recent history (last 6 months) of inadequate response to treatment with topical therapy, immunosuppressants, biologics or JAK-inhibitors.

∙ 9\. Current treatment can include moisturizers, topical treatment and/or systemic treatments with preferable wash-out (see exclusion criterion #9). On-study treatment is at physician and patient discretion but must include eligibility to starting new systemic treatment.

∙ 10\. EASI≥7 (moderate-to-severe disease) 11. At least one suitable target lesion at the discretion of the investigator 12. Intention to start treatment with cyclosporine A, dupilumab, tralokinumab, lebrikizumab or a JAK1-inhibitor (abrocitinib or upadacitinib)

∙ For patients with CLE:

∙ Participants must have a diagnosis of CLE, including SCLE, CDLE or LET that fulfil the following:

∙ 6\. Confirmed CLE diagnosis by clinicopathological correlation. 7. An overall CLE Disease Area and Severity Index Activity (CLASI-A) Score ≥3 without counting any diffuse alopecia or oral ulcers.

∙ 8\. Intention to start treatment with TCS, hydroxychloroquine or methotrexate (combination or mono-treatment).

∙ If participating in the exploratory study with the skin biopsy: location of the lesion(s) selected for biopsy preferably outside the facial area (possible are e.g., neck, chest, back, limbs, scalp, ear etc.).

∙ For patients with CSU:

∙ 6\. Diagnosis of CSU (moderate to severe according to international guidelines (Zuberbier et al, 2022)) for ≥3 months and symptomatic disease despite treatment with second generation H1 antihistamines (up to fourfold the approved dose).

• Patients currently on an antihistamine (up to fourfold the approved dose) must be on a stable dose for at least 2 weeks prior to day 1 and must maintain the same stable dose throughout the treatment period.

∙ 8\. Intention to start (add-on to antihistamine) treatment of omalizumab, cyclosporine A or BTK inhibitor\*. (\*when approved and reimbursed in NL)

∙ For patients with HS:

∙ 6\. Patient with a history of signs and symptoms consistent with moderate-to-severe HS, based on IHS4 score (Zouboulis et al., 2017), for at least 1 year prior to baseline 7. Current treatment can include topical treatment. On-study treatment is at physician and patient discretion but must include eligibility to starting systemic treatment 8. Intention to start treatment with anti-TNF or anti-IL17 (secukinumab, bimekizumab\*) \*when approved and reimbursed in NL.

∙ For patients with MF:

∙ 6\. A confirmed diagnosis of CTCL MF type and stage classification via histology or clinicopathological correlation 7. For the stage IA-IIA CTCL patients: at least one patch and/or one plaque lesion is present 8. Intention to start treatment with topical chlormethine, topical corticosteroids or phototherapy (PUVA / UV-B).

∙ For patients with PSO:

∙ 6\. Diagnosed with chronic plaque psoriasis at least 6 months prior to study participation 7. PASI≥5 with at least one suitable target lesion at the discretion of the investigator 8. Current treatment can include moisturizers, topical treatment and/or systemic treatments with preferable wash-out. On-study treatment is at physician and patient discretion but must include eligibility to starting new systemic treatment 9. Intention to start treatment with biologics: anti-TNF, anti-IL23, anti-IL17 or anti-TYK2

∙ Healthy volunteers:

∙ All healthy volunteers must meet all of the following inclusion criteria:

⁃ Signed informed consent before any study-mandated procedure.

⁃ Male or non-pregnant female volunteers, ≥18 years of age

⁃ Subject is in stable good health as per judgement of the investigator based upon the results of medical history and assessments performed at baseline.

⁃ No clinically significant skin disease as judged by the investigator.

⁃ No history of hypertrophic scarring or keloid.

⁃ Subject is willing to refrain from extensively washing (including bathing, swimming) the skin 12 hours before every study visit.

⁃ Subject is willing and able to wash out and withhold any topical treatment (prescription and over-the-counter products) in the investigational area for 2 weeks prior to Day 1.

⁃ Subject is willing to refrain from application of any topical product (e.g. ointments, cream, or washing lotions) on the skin 24 hours prior to every study visit day.

⁃ Subject is willing and able to wash out any antibiotic therapy for 14 days prior to Day 1.

‣ Subject is willing and able to comply with the study protocol.

‣ Female participants are willing to not get pregnant from study entry to the last study visit