A Longitudinal Study of the Facial Skin Microbiome in Normal Healthy Adults

Posted 3rd August 2018 by Jane Williams

Human skin is the largest organ that acts as a front line of defence against toxic effects from its exposure to toxic environmental factors^1-3. Skin Microbiome is considered an integral part of skin barrier that, combined with innate immunity, plays a key role in maintaining the skin health^4-7.

Like gut microbiome, skin is a home for transient, short-term and resident, long-term microbiota. However, there is limited knowledge on how the intrinsic and extrinsic host factors, such as genetics, hormonal balance and imbalance, lifestyle, diet, medications and cosmetics, influence their composition.

The foremost phyla of skin microbial community encompass Proteobacteria, Actinobacteria, Firmicutes, and Bacteroides, with Proteobacteria being the most abundant^{3, 8-11}. The most prominent genera belonging to these phyla is comprised of Propionibacterium, Corynebacterium, Staphylococcus, Micrococcus, Streptococcus, Brevibacterium and Malassezia that are described as follows^2-7:

1. Staphylococci (Firmicutes) – reside predominantly in the moist areas of the body, such as the armpit, the elbow crease, etc. As aerobic bacteria, they produce lactic acid that lowers the pH of the skin and controls the growth of other microorganisms.
2. Propionibacteria (Actinobacteria) – the most prevalent on sebaceous, or oily skin, such as nostrils, scalp, upper chest and back. They are lipophilic anaerobes, decomposing oily sebum secreted by our glands, producing propionic acid.
3. Corynebacteria (Actinobacteria) – innocuous and slow growing bacteria that prefer moist environments, such as the navel, or back of the knee.
4. Brevibacterium (Actinobacteria)¹² – epidermidis forms part of the resident flora of the human skin surfaces and probably contributes to unpleasant body odours.
5. Malassezia (Fungus)¹³ – found in copious quantities on human skin. These are typically harmless, but certain species can cause dandruff or skin discoloration.

Bacteria are known to be selective for their home and community. Therefore, different skin sites harbour distinct microbial populations at varied concentration, revealing their preference for dry, moist or sebaceous environment. Dry skin appears to exhibit more diversity in its microbial populations as compared to sebaceous skin and most skin sites that predominantly harbour lipophilic bacteria^{3, 14-16}. Culture based assays indicated their concentration may be as high as 10⁷cfu/cm² in moist areas, such as axilla or toe web space, and as low as <10²/cm² in dry areas such as forearms¹⁷.  Culture assays, due to their inherent limitation, only recover culturable microbes that flourish in favourable growth conditions.

New high-throughput sequencing of the 16S ribosomal RNA gene has been introduced. It enables the characterisation of bacterial communities at various body sites, which has provided new insights into the diversity of skin microbial community under normal conditions and any shifts in their community structure or balance from intrinsic or extrinsic influential factors.

Most of the skin microflora, whether residing on the skin surface or in the hair follicles, are characterised as gram positive microorganisms. For healthy skin, its natural mechanisms, such as hydration, nutrients, pH, antimicrobial peptides, play a crucial role in controlling the microbial diversity and maintaining the balance and dominance of beneficial resident microbes, while restricting the invasion of transient pathogens. Beauty and personal care products, generally chemical preparations, are designed to enhance and balance skin hydration, pH and nutrients¹⁸.

With the rise in consumer demand for more sophisticated, natural, age-defying cosmetics, as well as products to enhance the appearance of the skin to look younger, glowing, smooth, wrinkle and acne free, it is imperative to understand the relationship of skin microflora with visual facial signs of healthy skin.

To understand the impact of long term use of cosmetics on skin microbial community, we conducted a longitudinal study on 150 normal healthy men and women that took place between May 2017 and May 2018. In the study, we measured both visible facial features, such as wrinkles, hyper-pigmentation, porphyrins, and biophysical skin properties, including barrier function, skin surface pH and elasticity, to explore insights into how the skin microbiome composition changes with these signs of skin health and to help target the development of microbiome-based beauty products. The study is designed to collect data over a ten-year period to identify the visual signs of skin ageing, and wrinkles.

Kausar Malik is Senior Principle Research Scientist at Amway Corporation, Ada, Michigan.

Kausar Malik will be discussing the results from the Cinco de Mayo Study at the Microbiome R&D and Business Collaboration Forum: USA. Find out what else we’ve got in store by taking a look at the agenda.

See the full reference list here.

Tags: cosmetics, microbiome, skin health