The lips form a boundary between the skin and the oral cavity. Unlike facial skin with up to 16 layers of epithelial cells, the vermilion of the lip is only 3-5 layers thick and lacks sebaceous and sweat glands, making it susceptible to dryness.^1,2 The skin harbors a core group of bacterial species of the phyla Actinobacteria, Firmicutes, Proteobacteria, and Bacteroidetes.^3,4 Different skin niches, including moist, dry, and sebaceous areas, harbor these core phyla at different proportions and distinct levels of diversity.^3,4 The microbiome interacts with the immune system and protects the skin from infection^3,4 and is only beginning to be understood. While cutaneous skin microbiome has been studied, lip microbiome has not been previously characterized. To better understand this unique area of skin, we characterized the lip microbiome using metagenomics.

A subpanel of 19 women from a total of 45, ages 20-55, with none-to-mild self-perceived lip dryness who were enrolled in a monadic study to assess a lip care product, were randomly selected for lip microbiome collection. Participants were free from diseases or medications that might directly interfere in the study. Participants abstained from using facial moisturizing products for 2 days and any lip products for 3 days prior to and during the study period. The lip microbiome was assessed ribosomal RNA (rRNA) sequencing from lip swabs taken at the initial study visit after 30 minutes of equilibration. Informed consent was obtained for all study participants.

In our analysis of the lip microbiome, we identified at least twenty phyla. In order of abundance, the four predominant species belonged to Firmicutes (38%), Proteobacteria (23%), Actinobacteria (15%) and Bacteroidetes (12%) (Figure 1A). These four phyla constituted ~88% of the bacterial lip microbiome. The other abundant species belonged to Fusobacteria (6%).

Figure 1.

The microbial distribution of the lip microbiome from 19 healthy women is shown in Figure 1B. Of the 20 most abundant phyla found on the lip—comprising 90 percent of the of bacterial flora species identified—six species belonged to Firmicutes, five species belonged to Proteobacteria, seven species belonged to Actinobacteria, and one each belonged to Bacteroidetes and Fusobacteria. In general, a large interpersonal variation in microbial community was observed.

As a first step in characterizing the human lip microbiome, our results demonstrate that the lip microbiome is similar to the skin microbiome, with dominant representation of Actinobacteria, Firmicutes, Proteobacteria, and Bacterioidetes.^3,4 The proportions of these resident phyla appear distinct from other skin niches. Our analysis revealed a small but measurable population of spirochaetes, a phylum of oral bacteria frequently associated with periodontitis.⁵ It remains to be determined whether pathogenic oral bacteria can affect lip health, especially considering that lip-licking associated with dryness could transport oral bacteria to the lip. Research has shown that alterations in the composition of the skin microbiome may influence the pathogenesis of dermatological disorders.^3,4 Dryness and chapping are associated with altered composition and thickness of the surface corneocyte layer²; whether this permits an altered microbiome is a question for future research. How lip care and makeup products affect the lip microbiome remains to be determined. The limitations of this study include the small sample size, inclusion of only female participants and assessment at only one time point. This leaves a gap in establishing whether the lip microbiome varies with gender and whether there may be personal variation in the lip microbiome across time. Further investigation and additional studies must continue in this area.

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