The microbiome of the gut and skin can impact one another in health and disease. Numerous dermatologic disorders can be traced to gastrointestinal etiologic origins.1 Incorporating discussion of the latest findings on the cutaneous and gut microbiome expands our understanding of the origin of dermatologic disease., but the gut microbiome also has effects on the skin microbiome that are just being elucidated. Although we do not yet know enough to give our patients definitive advice about probiotics, the knowledge in this field is rapidly expanding and is an exciting area to watch. Certainly, everything applied to the skin or ingested in the diet plays a role in the skin and gut microbiome. Therefore, the savvy dermatologist understands that personal care products, including cosmeceuticals, will affect the microbiome. At this point, we do not yet know what is beneficial, but we do know that diversity of organisms is important and is the preferred state as compared to having fewer types of organisms on the skin.
Acne has long been known to have a multifactorial etiologic pathway. It is increasingly thought that understanding the role of the skin (and possibly gut) microbiome in acne pathophysiology may lead to enhanced treatments.2 New gene sequencing technologies, particularly those based on recA and tly loci, are teaching us more about the anaerobic bacterium Propionibacterium acnes (now called Cutibacterium acnes).3
In 2017, Dréno et al. studied the skin microbiota in 26 subjects with mild to moderate acne. The microflora were characterized using a high‐throughput sequencing approach that targets a portion of the bacterial 16S rRNA gene. The samples were obtained before and after 28 days of treatment with erythromycin 4% or a cosmeceutical containing lipohydroxy acid, salicylic acid, linoleic acid, niacinamide, piroctone olamine, a ceramide, and thermal spring water. Upon conclusion of the study, Actinobacteria were reduced in both groups while staphylococci were reduced only in the dermocosmetic group.4 The interesting point of this study was that the cosmeceutical had a greater impact on staphylococci than did topical erythromycin, demonstrating that personal care products can have profound effects on the microbiome.
Early in 2018, Kelhälä et al. compared the impact of the systemic acne treatments isotretinoin and lymecycline on cutaneous microbiota in the cheeks, back, and axillae of mild to moderate acne patients using gene sequencing. They found that acne severity positively correlated with Propionibacterium acnes levels. P. acnes levels were decreased by both treatments, but isotretinoin resulted in a greater decrease. Increased microbiome diversity was seen on the cheek and back in all treated subjects, but diversity was highest in those treated with isotretinoin.5 The authors postulated that the diversity resulted from a decrease in P. acnes levels. To learn more about what to tell your patients about acne and the microbiome, read my