Origanum vulgare L. Essential Oil as a Potential Anti-Acne Topical Nanoemulsion—In Vitro and In Vivo Study

Antibiotics are often prescribed in acne treatment; however, <i>Propionibacterium acnes</i> and <i>Staphylococcus epidermidis</i>, the two of the major acne-associated bacteria, developed antibiotic resistance. Essential oils (EOs) present a natural, safe, efficacious and multifunctional alternative treatment. This study aimed to assess the potential anti-acne activity of selected seven EOs commonly used in Mediterranean folk medicine. Antimicrobial activity screening of these oils showed oregano to exhibit the strongest antimicrobial activity with minimum inhibitory concentration (MIC) of 0.34 mg/mL and minimum bactericidal concentration (MBC) of 0.67 mg/mL against <i>P. acnes</i>; and MIC of 0.67 mg/mL and MBC of 1.34 mg/mL against <i>S. epidermidis</i>. The composition of the most effective EOs (oregano and thyme) was determined using gas chromatography-mass spectrometry (GC-MS). Monoterpenoid phenols predominated oregano and thyme EO with thymol percentile 99 and 72, respectively. Thymol showed MIC 0.70 mg/mL against both <i>P. acnes</i> and <i>S. epidermidis</i> whereas MBC was 1.40 and 2.80 mg/mL against <i>P. acnes</i> and <i>S. epidermidis</i>, respectively. Moreover, oregano exhibited the strongest anti-biofilm effect against <i>S. epidermidis</i> with MBIC 1.34 mg/mL and killing dynamic time of 12 and 8 h against <i>P. acnes</i> and <i>S. epidermidis</i>, respectively. Oregano, the most effective EO, was formulated and tested as a nanoemulsion in an acne animal mouse model. The formulation showed superior healing and antimicrobial effects compared to the reference antibiotic. Collectively, our data suggested that oregano oil nanoemulsion is a potential natural and effective alternative for treating acne and overcoming the emerging antibiotic resistance.