A Study to Assess Molecular Changes in Adult Participants With Moderate to Severe Hidradenitis Suppurativa or With Moderate to Severe Atopic Dermatitis Receiving Subcutaneous Injections of Lutikizumab

Inclusion Criteria: * Sub-Study 1 hidradenitis suppurativa (HS): * Participants with a diagnosis of moderate-to-severe HS for at least 6 months prior to Baseline as determined by the investigator * Participants naïve to biologic treatment for HS or must have a prior inadequate response or loss of response to anti-TNF therapy for HS (\>= 12 weeks of therapy). * Sub-Study 2 atopic dermatitis (AD): * Participants with a diagnosis of moderate-to-severe AD with onset of symptoms at least 1 year prior to Baseline. * Participants naïve to biologic treatment for AD or must have a prior inadequate response or loss of response to dupilumab for AD (defined as \>= 8 weeks of therapy with dupilumab). Exclusion Criteria: * History of any malignancy within the last 5 years except for successfully treated nonmelanoma skin cancer (NMSC) or localized carcinoma in situ of the cervix. * History of active skin disease (other than HS for Sub-Study 1 or AD for Sub-Study 2) that could interfere with the assessment of HS (for Sub-Study 1) or AD (for Sub-Study 2), including skin infections (e.g., bacterial, fungal, or viral) requiring systemic treatment within 4 weeks of the Baseline.