In a mouse model of acne, adding bacteriophages (viruses that kill acne‑causing bacteria) to the skin reduced the size of inflammatory nodules more than just the bacteria alone, and also lowered some skin changes linked to acne. The study showed that the usual acne‑related immune markers, including the peptide LL‑37, stayed the same across groups, suggesting the phages work without dramatically altering the skin's immune response.

Bacteriophages have been introduced as living drugs for infectious diseases; thus, they may provide an alternative to conventional acne therapeutics in patients with non-responsive acne. We investigated the effect of bacteriophages using an acne mouse model with <i>Propionibacterium acnes</i>-induced inflammatory nodules by clinical examination, pathology, and immunohistochemical analysis. A human-isolated <i>P. acnes</i> suspension (10⁹ colony forming units/&#xb5;l) was injected into the backs of HR-1 mice. Group A was used as a control, Group B was injected on the back with <i>P. acnes</i> 4 weeks following the initial <i>P. acnes</i> suspension injection, and group C was injected on the back with <i>P. acnes</i> and bacteriophages 4 weeks following the initial <i>P. acnes</i> suspension injection. Clinical and histopathological evaluations were performed. Inflammatory nodule size decreased with time in all groups. Group C showed the greatest decrease in size, followed by group B and group A. The histopathological findings showed a decrease in epidermal thickness and the number and size of microcomedone-like cysts in groups B and C compared to group A. Immunohistochemistry revealed similar expression of integrin &#x3b1;6, the epidermal proliferation marker, infiltration of CD4/CD8 T cells and neutrophils, and expression of myeloperoxidase, interleukin-1&#x3b2;, toll-like receptor-2, LL-37, and matrix metalloproteinase-2/3/9 in all three groups. Using an acne mouse model with <i>P. acnes</i>-induced inflammatory nodules, we demonstrate that bacteriophages may constitute an alternative to conventional acne therapies. However, additional studies are needed for human applications.