Skin and hair microbiomes were put under the microscope during a seminar developed by the New York Chapter of the Society of Cosmetic Chemists (NYSCC). The event was developed and moderated by session chair Mythili Nori of BASF.

Nutrafol’s Nicole Townsend opened the evening with a virtual presentation on the scalp microbiome and implications for formulating hair care products. She reviewed the hair lifecycle stages: anagen, catagen, telogen and exogen. Townsend reviewed dysbiosis of the gut and hair. Intestinal permeability, aka “leaky gut,” leads to increased permeability of toxins and low-grade systemic inflammation that can affect hair follicles.

“Increased levels of pro-inflammatory cytokines are known mediators implicated in hair loss,” noted Townsend.

The Gut/Scalp Interface

At the same time, poor nutrition and breakdown due to a dysfunctional gut detracts from metabolic processes involved in hair synthesis. Townsend turned her attention to two relatively new areas of research. The scalp microbiome acts as a shield to the scalp, providing protection for a strong scalp barrier and healthy hair quality. The hair follicle microbiome regulates the immune system and interacts with cells that influence hair growth and formation.

Some of the intrinsic and extrinsic factors that affect the skin microbiome include oxygen access, pH, temperature, moisture and sweat levels, lipid content, age, sex, climate, lifestyle and genetic predisposition.

“The scalp microbiome is different than the skin microbiome,” she noted.

For example, the scalp has the highest hair follicle density compared to the rest of the body. It produces large amounts of sebum. And it has unique oxygen availability, moisture content and pH. As a result, the scalp is uniquely colonized by Cutibacterium, Malassezia and Staphylococcus. Too little diversity in the scalp microbiome leads to an imbalanced scalp and corresponds to a range of conditions, including dry scalp, flaky and itchy scalp, red and irritated scalp, damaged hair before it emerges from the scalp, and overproduction of sebum and oily scalp.

In a clinical study investigating the correlation of between sensitive scalp biophysical properties, sebum composition and production yields, the sensitive scalp group showed:
• Higher pH;
• Irritated skin (self-perceived);
• Increased sebum production;
• Higher percentage of Propionibacterium; and
• Lower overall bacterial diversity.


“The scalp micro-environment is linked to altered hair quality,” noted Townsend. “When the micro-environment of the scalp is altered, it can impact the quality of the emerging hair.”

For example, imbalance in the microbiome can lead to increased oxidative stress on the scalp and hair follicle. Oxidative stress alters the ability of the hair follicles to protect growing hair. The impact of an imbalanced scalp can result in compromised hair cuticle integrity. Furthermore, shifts within the hair follicle microbiome are linked to scalp disorders such as seborrheic dermatitis, androgenetic alopecia, alopecia areata, folliculitis decalvans and scalp psoriasis, concluded Townsend.

Formulating Microbiome-Friendly Products

Allison Gartlet, BASF, reviewed microbiome basics and gave an overview of the complex interactions that take place within the microbiome.

“Different body sites have different microbiome compositions,” she noted.

Skin nutrient levels are relatively low compared to other areas of the body. The major nutrients on skin are sweat, sebum and stratum corneum components such as lipids and peptides. The dominant microbial groups include Staphylococci, Cutibacteria, Corynebacteria and Malassezia. These residents can be divided into two groups—commensal bacteria, which lives in harmony with skin cells, and opportunistic pathogens, which evade the immune system and cause irritation.

Gartlet reviewed a clinical study design, sampling strategy and sequencing strategy.

In an invitro study method, the bacteria and personal care ingredient are combined to identify inhibition of bacterial growth. Skin cells are combined with the bacteria and the personal care ingredient and the biofilm formation by the bacterial strain is reviewed. In the in vivo model, the microbiome sample analysis is performed by metagenomic sequencing.

“Sequency represents a great deal when talking about microbiome,” noted Gartlet.

Why is a balanced microbiome good for skin and scalp? One, it supports healthy skin, which fosters the environment for healthy microflora. Two, it supports skin’s surveillance—a healthy microbiome is the body’s first line of defense against pathogens.

Gartlet reviewed microbiome approaches in personal care and provided definitions for each product type. Prebiotics are substrates that are selectively utilized by the host microorganisms conferring a health benefit. Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. Finally, postbiotics are non-viable bacterial products or metabolic byproducts from probiotic microorganisms that have biological activity in the host.

“We’re moving toward whole ‘microbiome-friendly’ formulations for personal care,” insisted Gartlet. “These formulations combine microbiome-friendly functional ingredients with active, hero ingredients.”

The products can have anti-aging, moisturizing, soothing effects, boost efficacy and protect skin.

“Focusing on the microbiome enables formulators to go beyond simple skincare benefits like hydration to advanced benefits for skin health,” she concluded.

Next Generation Skincare Formulas

L’Oréal Senior Scientist Amina Bouslimani noted it’s been 15 years since the Human Microbiome Project was launched by the US National Institutes of Health to improve understanding of the microbiota involved in human health and disease. Today, we know that bacteria accounts for more than 50% of skin and that there are more than 1000 bacterial species.

The skin microbiome is shaped by body site; Staphylococcus and Corynebacterium spp. are the most abundant organisms colonizing moist areas. The most diverse skin sites are the dry areas, with mixed representation from phyla Actinobacteria, Proteobacteria, Firmicutes and Bacteriodetes.

When in balance, the skin barrier is physical, immune and microbial, and regulates skin function and appearance. These microbes live among one another and “cross-talk,” explained Bouslimani. “It’s all a function of healthy skin,” she said.

Microbiome dysbiosis may lead to skin alterations. In cases of severe atopic dermatitis (AD), S. aureus levels rise; in less severe AD cases, S. epidermis levels rise. In acne, C. acnes virulent prototypes and S. epidermis levels rise. In psoriasis, Brevibacterium, C. Stumulans and C. Kroppenstedtii levels rise. Meanwhile, in rosea, C. acnes levels decline, while Snodgrassella alvi rise.

“It is balancing act between harmful/opportunistic bugs and beneficial/commensal bugs,” explained Bouslimani.

But the balancing act gets altered with age—there’s a different bacterial signature in those 60+. Changes include greater diversity of microbes, along with lower C. acnes levels. Where one lives alters the microbiome, too. Those who live in rural areas have more diverse microbiomes. In highly polluted areas, young women with premature skin aging have a microbiome signature close to that of old women.

“Metabolites are the key to understanding the microbiome,” Bouslimani noted.

To modulate the skin microbiome with cosmetics, formulators can work with traditional prebiotic and postbiotic materials. The more challenging opportunities lie in bio-derived materials (such as peptides and enzymes), phages (virus infecting and killing bacteria) and probiotics (live bacterial strains).

She reviewed several studies demonstrating the efficacy of these materials. For example, S. Aureus specific endolysin produces strong and fast eczema improvement (70%) in adults and children.

“There are expanding applications for live bacteria, but we are at the tip of the iceberg,” Bouslimani noted. “We must translate the knowledge we have on the microbiome into products.”

Ongoing challenges include formulating stable product that include live bacteria and having the right in vitro model that can mimic the microbiome.

“It’s not impossible. It’s about finding the right technology with the right ingredients that don’t interference with bacterial growth,” concluded Bouslimani. “We may start seeing these products in the next few years.”