In Vitro Antimicrobial Activity and In Vivo Effectiveness of the Cosmetic Products Developed for Oily Skin

<strong>Background and Aims:</strong> This study aimed to evaluate the<em> in vitro </em>antimicrobial activity and in vivo effectiveness of three cosmetic products designed for cleansing (Facial Cleansing Foam), toning (Facial Toner), and moisturising (Moisturising Gel-Cream) as part of a facial care regimen for oily and acne-prone skin. <strong>Methods:</strong> The in vitro antimicrobial activity of the formulations was tested against <em>Cutibacterium acnes</em> (formerly <em>Propionibacterium acnes</em>), <em>Staphylococcus epidermidis</em>, and <em>Staphylococcus aureus </em>using standard <em>in vitro</em> tech niques. The in vivo effectiveness was assessed through non-invasive biophysical methods, examining both a single application and a 4-week period of use. Measurements included transepidermal water loss (TEWL), skin hydration, melanin levels, erythema, skin pH, and sebum levels in healthy human volunteers. <strong>Results:</strong> In vitro tests demonstrated that the Facial Cleansing Foam achieved a ≥3-log10 reduction in bacterial count within a maximum of 4 h, effectively inhibiting all three tested pathogens. In the in vivo cosmetic efficacy study, short-term results indicated that the products maintained TEWL levels within the “very healthy” range. Long-term results over 4 weeks revealed a statistically significant reduction in TEWL, along with a notable improvement in skin hydration. Extended use of the products indicated potential benefits in enhancing skin tone uniformity and maintaining skin surface pH balance. Additionally, sebum production on the face significantly decreased after four weeks, highlighting the products’ effectiveness in controlling facial oiliness. <strong>Conclusion: </strong>The Facial Cleansing Foam was the most effective formulation in the<em> in vitro</em> antimicrobial study, demonstrating efficacy against all tested pathogens. The Facial Toner effectively controlled bacterial growth for 24 h, while the Moisturising Gel-Cream showed this effect only against <em>C. acnes</em>. Beyond antimicrobial efficacy, all three products led to significant improvements in skin biophysical parameters, particularly in reducing sebum levels, with the most pronounced effects observed after 4 weeks of use.