This study looks at a new medicine called UCB1381 for people with atopic dermatitis, also known as eczema. Eczema is a skin condition that makes skin itchy, red, and swollen. The study is divided into two parts. Part A includes healthy people aged 18 to 55, while Part B includes people aged 18 to 65 with moderate to severe eczema. In Part A, healthy participants will receive a single dose of UCB1381, either through a needle in the vein (intravenous) or under the skin (subcutaneous), to check if it's safe. In Part B, people with eczema will get repeated doses of the medicine to see if it helps their skin condition compared to a placebo, which is a "fake" treatment. Participants must meet specific health criteria and agree to use birth control during the study.

• Study Duration: The study involves multiple visits over several weeks.
• Compensation: Participants may receive payment for their time and travel.
• Risks: Possible side effects include allergic reactions or skin irritation.