Effects of Abrocitinib Treatment on Skin Barrier Function

Inclusion Criteria:

1. Written informed consent obtained from the subject prior to performing anyprotocol-related pro-cedures, including screening evaluations

2. Age ≥ 18 years at time of study entry.

3. Diagnosis of chronic atopic dermatitis for at least 1 year prior to enrollment basedon American Academy Criteria

4. Eczema Area and Severity Index (EASI) score ≥12 at baseline visit (Week 0)

5. Investigator Global Assessment (IGA) ≥3 at baseline visit (Week 0)

6. Subject is willing and able to comply with the protocol for the duration of thestudy

7. Subject receives abrocitinib by the treating dermatologist within routine care

Exclusion Criteria:

1. 1. Subject is unable to provide written informed consent or comply with the protocol

2. Concurrent enrolment in another clinical trial where the subject is receiving an IMPor participation in another clinical trial with investigational product during thelast 30 days before inclusion or 7 half-lives of previously used trial medication,whichever is longer.

3. Active dermatologic conditions that may confound the diagnosis of AD or wouldinterfere with as-sessment of treatment, such as scabies, cutaneous lymphoma, orpsoriasis.

4. Known active allergic or irritant contact dermatitis that is likely to interferewith the assessment of severity of AD.

5. Having used systemic immunosuppressive/immunomodulating therapy (e.g. systemiccorticoster-oids methotrexate, cyclosporine, azathioprine, mycophenolate mofetil,JAK inhibitors) or tanning beds or phototherapy during any week within the 4 weeksor receipt of any marketed biologic ther-apy (e.g., dupilumab, tralokinumab) within 3 months or 5 half-lives, whichever is longer, prior to baseline

6. Treatment of selected marker skin areas (non-lesional skin at volar forearm andextensor forearm, lesional skin) with topical corticosteroid or topical calcineurininhibitor 1 week prior to baseline visit and throughout the study.

7. Treatment of skin areas of examination with emollients 24 hours prior to baselinevisit and throughout the study.

8. Involvement in the planning and/or conduct of the study.