The purpose of this study is to evaluate the potential improvement in atopic dermatitis signs and symptoms following the application of FB-401 in patients 2 years or older with mild to moderate atopic dermatitis. FB-401 will be applied topically for 16 weeks and progress will be assessed by assessment of the skin and patient reports.

Inclusion Criteria:

• Male or female, ≥ 2 years of age
• Clinical diagnosis of atopic dermatitis as defined by Hanifin and Rajka criteria that has been present for ≥ 3 months before the screening visit
• Investigator Global Assessment (IGA) score of 2 (mild) or 3 (moderate) at Screening and Baseline/Day 1 using the validated IGA scale for atopic dermatitis
• EASI score ≥ 5 at the screening and the Baseline visit
• 5% to 30% (inclusive) body surface area of atopic dermatitis involvement at the screening and the baseline visit

Exclusion Criteria:

• Previous treatment within 4 weeks prior to the baseline visit with any of the following:
• Immunosuppressive or immunomodulating systemic drugs such as systemic (intravenous, oral, intra-articular or intramuscular) corticosteroids, azathioprine, methotrexate, cyclosporine
• Phototherapy or photo chemotherapy for atopic dermatitis
• Previous treatment within 1 week prior to the baseline visit with any of the following:
• Topical corticosteroids (does not include inhaled, intranasal or ophthalmic) or topical calcineurin inhibitors
• Topical phosphodiesterase type 4 (PDE4) inhibitor
• Use of emollients other than provided for the study
• Bleach baths
• Within 8 weeks or 5 half-lives (if known), whichever is longer, prior to the baseline visit with Janus kinase inhibitors or other investigational drug
• Within16 weeks or 5 half-lives, whichever is longer, prior to the baseline visit with dupilumab or other biologic agent to treat atopic dermatitis
• Within 1 year prior to the baseline visit with any live bacterial therapy
• Pregnant (or planning to become pregnant during the period of the study) or lactating females