This study will enroll a minimum of 20 participants, 18-80 years of age, with moderate-to-severe atopic dermatitis (AD) on their ventral arms. A minimum of 13 participants will have a positive Staphylococcus aureus (S. aureus) colonized lesion on both upper extremities. A minimum of 7 participants will have a negative S. aureus colonized lesion on both upper extremities.~The participant's colonization status will be determined from cultures taken during a pre-treatment phase, approximately 7 days prior to receiving study treatment on Day 0. On Day 0, skin swabs will be collected from lesional and non-lesional sites (at least 21cm^2) on the participant's right and left ventral arms and one non-lesional site on the participant's face. After the skin swab collections, the participant will have ShA9 applied to their right or left ventral arm and placebo applied to their contralateral ventral arm. The assignment of ShA9 and placebo to the dominant and non-dominant arms will be randomized. Additional swabs will be collected 15 minutes, and 1, 2, 4, and 6 hours after the ShA9 and placebo applications on Day 0.~Participants will be asked to return to the clinic 24 hours after receiving their single application and again on Days 3, 10, 17, and 24 for the assessment of adverse events (AEs) and the collection of skin swabs from the identified lesional and non-lesional sites, as needed. After the Day 3 visit, a participant will not be required to complete the Day 10, 17, and 24 visits if their lesional swabs are negative for Coagulase Negative Staphylococcal Species (CoNS).~All randomized participants will complete a final End of Study Phone visit on Day 31 to assess for adverse events and status of their AD.
The purpose of this study is to examine the pharmacokinetics or survival of new product containing commensal infection fighting bacteria, on the skin of patients with Atopic Dermatitis (AD), after a single application.