A growing body of evidence suggests that the development and progression of acne are closely linked to an imbalance in the skin's microbial community. Compared to healthy skin, the composition and function of the microbiota in acne lesions are significantly altered. This microbial imbalance is believed to drive the formation and recurrence of acne through mechanisms such as triggering abnormal inflammatory responses and compromising the skin barrier.

An in-depth exploration of the interaction between acne and the skin microbiome not only offers new perspectives for understanding the root causes of the disease but also lays the groundwork for developing novel treatment strategies aimed at modulating the microbiota. Therefore, identifying innovative approaches that integrate acne treatment with the regulation of microbial balance holds significant clinical and social value.

Although existing acne treatments have made progress, research focusing on interventions that regulate the local skin microecology through probiotics remains relatively limited. This study aims to explore a new strategy based on skin microecological modulation. Investigators are using a common probiotic-Lactobacillus reuteri-and applying an engineering modification with a special coating formed by zinc sulfate and tannic acid (MPN coating). This modification is intended to enhance the bacterium's survival and colonization on the skin, thereby more effectively regulating the local microbiota and reducing inflammation.

This study is a rigorous scientific clinical trial designed as randomized, double-blind, and controlled. Eligible participants will be randomly assigned to one of four groups, receiving either the engineered Lactobacillus reuteri cream, the plain Lactobacillus reuteri cream, a simple moisturizing cream (placebo), or an already-marketed effective cream (tretinoin cream). The treatment will last for 2 weeks, followed by an 8-week observation period. Efficacy and safety will be evaluated through professional assessments.

Our goal is to scientifically evaluate the safety and efficacy of this new therapy, hoping to provide a potential new treatment option for individuals with acne and explore new pathways for improving skin health.

Inclusion Criteria:

1. Subjects must be diagnosed with acne (based on history, clinical manifestation, and dermatoscopy) and classified as Grade I to III per the International Improved Grading System.
2. Subjects must be willing and able to provide written informed consent.
3. Subjects must be 18 to 33 years of age and in generally good health.
4. Subjects must have more than 9 inflammatory lesions.

Exclusion Criteria:

1. Have used antibiotics within 1 month before the study start.
2. Have used systemic retinoid therapy within 3 months before the study start.
3. Have undergone any other acne treatment within 1 month before the study start.
4. Have any other condition that the investigator considers would make participation unsuitable (e.g., deemed unreliable, non-compliant, or unable to comprehend the study assessments).