This study is for teens aged 12-17 with moderate to severe Hidradenitis Suppurativa (HS). HS is a skin condition that causes painful lumps under the skin. The study will look at how a medicine called sonelokimab works and if it's safe. Sonelokimab is given through a small needle under the skin. To join, participants need to have tried antibiotics for HS that didn't work well. They also need to weigh at least 40 kg (about 88 pounds) and have had HS symptoms for at least 6 months. Some kids can't join if they have too many fistulas, which are small tunnels under the skin, or other skin issues. Kids with certain health problems or allergies to the medicine can't join either.

• The study is open-label, meaning all participants will know they are getting sonelokimab.
• Participants must meet certain health criteria to join.
• Safety and how the body processes the medicine will be checked.