The study objective is to characterize the shift in the diversity and abundance of the skin microbial community at baseline and in response to Altreno monotherapy as compared to benzoyl peroxide (BPO) 2.5% leave-on gel monotherapy in acne patients.

With the advent of 16S rRNA sequencing, scientific community is beginning to understand the critical importance of the microbiome in human health. In dermatology, researchers have begun to lead the effort to not only better understand how the microbiome contributes to the pathogenesis of skin disease, but also harness its power to develop novel therapies. Acne is a common inflammatory skin disorder. P. acnes on the skin has been traditionally thought of as the culprit bacteria in the pathogenesis of acne.

Recent studies demonstrate that the skin microbial composition dynamically changes in response to systemic acne therapy. Using 16 rRNA gene sequencing, a prior study has confirmed that systemic antibiotic treatment decreased the abundance of P. acnes, which returned to baseline after discontinuation of the therapy. In contrast, the systemic therapy increased the abundance of Pseudomonas species, which returned to baseline after therapy cessation. Based on the opposing response to the therapy, it can be speculated that these two species compete for the same microenvironment within the skin microbiome. Interestingly, the same systemic therapy decreased the abundance of lactobacillus genus, the "good bacteria" that is protective against skin infection, and that decrease was sustained even after cessation of the therapy. Similarly, another study has demonstrated that systemic isotretinoin therapy disturbed the skin microbiome in acne patients with increased bacterial diversity on the cheeks. It is unclear the potential therapeutic role of the increased bacterial diversity in the management of acne patients.

The study aims to characterize the shift in the diversity and abundance of the skin microbial community in response to Altreno in acne patients. Understanding the role of the skin microbiome in response to therapy can help clinicians to develop tailored, targeted treatment options, including reconstitution of "good bacteria." Furthermore, it can lead to development of novel topical pre and probiotics.

Inclusion Criteria:

• A confirmed diagnosis of acne that warrants initiating topical medications.
• Denies use of any prescribed systemic acne treatments in the past 30 days.
• Denies use of any prescribed topical medications in the past 30 days.
• Denies use of any OTC topical acne medications in the past 14 days.
• Denies use of any emollients in the past 24 hours (if feasible).
• Denies bathing or facial washing in the past 12 hours (if feasible).
• Willingness to adhere to the recommended topical regimen during the duration of the study.

Exclusion Criteria:

• Women who are pregnant, breastfeeding, or planning to get pregnant during the study.
• Use of any investigational drug(s) in the past 3 months.

As described in the Pre-Assignment Details section, BPO arm was excluded from the study. We did not pursue processing the samples from 1 recruited subject in this arm. Therefore, we do not have any results to report.

The adverse events were asked at each study visit. For both groups, adverse events were collected over ~120 days.

• BPO arm only have 1 participant, so we decided to drop this arm.
• Small sample size, high drop out rate, and high failure rate of DNA extraction were the limitations of this study among others.