Skin Microbiomes and Skin Health

The skin is the largest organ of the human body. Beyond the naked eyes, the skin is the home to millions of bacteria, fungi and viruses that are beneficial to us. When the skin is covered and colonised by these microorganisms, they behave as a protective barrier against invasion of external insults and pathogens.  

When there is a disequilibrium of the microenvironment of these commensal microorganisms, the physical skin barrier can be disrupted, following more growth and invasion of pathogenic microorganisms. This can result in chronic inflammatory skin conditions or even more severe systemic medical conditions.

In this article, we discuss skin microbiomes and their associated with common skin conditions, making sense with current existing clinical treatment and exploring the potential role of understanding skin microbiomes in future treatment of skin diseases.

What are the microbes that I can find on my healthy normal skin?

Our skin is made up of two main layers: the epidermis (the external layer) and dermis (the inner layer). The epidermis is made up of keratinocytes that are crosslinked together to function as a physical barrier against the external world.

We can sub-classify the skin areas broadly into 3 areas: 

• the face/chest/upper back which is oily, 
• the flexures and folds of the elbows/knees/groin which are moist and 
• the back of arms and legs which are dry.

Common bacteria that can be seen in the oily area of a normal skin include propionibacterium acne spp. Fungi such as Malassezia spp and Candida spp can be found in oily regions of the skin as well. In moist areas, bacteria such as Staphylococcus spp and Corynebacterium spp can be seen. In dry areas of the skin, Staphylococcus spp can also commonly be seen.

Interestingly our skin microbiomes change from birth to puberty/adulthood. Newborns that are delivered through C-section tend to have skin microbiomes of normal skin while newborn that are delivered vaginally tend to have skin microbiomes that are also found in the vaginal lining. The prepubertal skin microbiomes have a greater population of Staphylococcus spp and Streptococcus spp.  The population of microbiomes shifts and remodels during pubertal period as the skin becomes oilier following hormonal stimulation of the sebaceous glands. With that, in pubertal and adult skin, there are more thriving Propionibacterium spp, Corynebacterium spp, Malassezia spp etc.

What factors change the normal skin microbiome?

The skin microenvironment is kept in equilibrium by multiple factors such as temperature and humidity, pH, UV exposure, sebaceous oil production, etc. The accessorial tissues around the skin such as the sweat glands, sebaceous glands and hair follicles ensures the microenvironment is being maintained.

Unfortunately, over time with the process of ageing, immunity changes, external insults such as strong contactant, allergies and etc, disruption of the skin microbiomes equilibrium can happen, with more ‘bad’ bacteria and less ‘good’ bacteria colonising the skin, resulting in various skin diseases.

The Association Between Skin Microbiomes and Chronic skin diseases — How do we translate this to current clinical practices?

Acne

Acne vulgaris is the most common chronic skin inflammatory disease after atopic dermatitis in the world. Acne occurs when there is inflammation of the skin resulting from blockage and excessive sebum production on the skin follicles. While the actual mechanism remains much elucidated, it is documented that one with acne has more colonisation of bacteria Propionibacterium acne (also known as cutibacterium acne). It is believed that Propionibacterium acne plays a role in comedone formation and the inflammatory process in acne.

Decreasing the amount of Propionibacterium acne has been shown to be beneficial in many acne patients and the idea is used as a target mechanism in the treatment of acne. Treatment options such as benzoyl peroxide, azelaic acid, antibiotics such as doxycycline, clindamycin and erythromycin can reduce the colonisation and inflammation caused by Propionibacterium acne. 

Rosacea

Rosacea is a chronic adult skin condition presented with recurring facial flushing, redness, pimple-like bumps. While the actual cause of rosacea remains unknown, microbiome mite- Demodex folliculorum is implicated in rosacea. Studies have shown that skin biopsy samples of rosacea patients have a high load of Demodex on inflamed affected skin, suggesting the link of the mite and the skin condition. Permetrin cream or oral ivermectin are offered as part of management of rosacea to reduce the colonisation of demodex mites on rosacea skin.

Atopic dermatitis / Eczema

Atopic dermatitis- presenting with chronic relapsing itchy, dry, red rashes is the most common skin condition worldwide which has a major negative impact on a person’s quality of life. The condition can be associated with other atopic conditions such as allergic rhinitis and asthma. While there is genetic predisposition and family history in atopic dermatitis, the distribution of skin microbiomes in atopic dermatitis may have its effect on a person’s clinical outcome.

Staphylococcus aureus has been well documented as a colonizer in atopic dermatitis. There is a correlation between the amount of the bacteria and the severity of the disease. The higher the density of the colonization of Staphylococcus aureus, the graver the inflammation. There is disruption of the normal microbiome skin environment in atopic dermatitis due to excessive colonization of Staphylococcus aureus. This results in impairment of skin barrier and susceptibility to other infections. 

In order to reduce colonization of Staphylococcus aureus, antibiotics (in the form of oral or topical) and bleach baths are used to manage eczema. Such treatment regimens can synergize the treatment outcome with conventional treatment of emollient, topical anti-inflammatory and systemic oral medications. 

Seborrheic dermatitis

Seborrheic dermatitis is a skin relapsing inflammatory condition affecting areas that are rich in sebaceous glands such as the face, scalp and body. One may notice the common exacerbating triggers such as hot weather, increase humidity, emotional heighten- which may all increase further production of sebaceous oil.

Fungi such as Malassezia spp are found in oily skin surfaces, and play a role in inflammatory response in seborrheic dermatitis. Antifungal treatment is used in combination with anti-inflammatory medication to effectively manage seborrheic dermatitis.

Is there a role for probiotics or prebiotics for skin conditions?

Probiotics are live microorganisms that when being introduced into the body sufficiently, produce a positive health outcome to the person. Prebiotics on the other hand are non-digestible food substances that can encourage the person to produce selectively certain ‘good’ bacteria in the body. Over the past decades, both probiotics and prebiotics are being marketed for their potential benefits in a person’s health for a wide range of diseases including gut symptoms such as irritable bowel syndrome, diarrhoea, to even treating vaginal infections.

For the context of skin, there is medical literature looking into the role of probiotics and prebiotics in atopic dermatitis, focusing more on children rather than adults. Studies for the role of these potentially beneficial supplements are still lacking for other common skin conditions such as psoriasis, acne, rosacea, etc. 

At this stage, probiotics and prebiotics are not considered a medical intervention for skin conditions. As a consumer or patient, one should be prudent in considering probiotics and prebiotics to avoid spending unnecessarily for non-clinically proven treatment due to marketing gimmicks. 

What have I learnt today?

• The skin microbiome can affect general skin health.
  
• Healthy skin microbiomes provide a shielding barrier against external insults and pathogens, keeping the skin and body healthy.
  
• There are associations of disequilibrium of skin microbiomes and some chronic skin inflammatory disease.
  
• Medical treatment targeting pathogenic microbiomes and aiming to restore normal skin microbiomes may be beneficial in management of chronic skin disease.
  
• There are inadequate clinical studies to prove the effectiveness of probiotics and prebiotics in skin health.

References:

1. Byrd, A., Belkaid, Y. & Segre, J. The human skin microbiome. Nat Rev Microbiol 16, 143–155 (2018).
2. Ellis SR, Nguyen M, Vaughn AR, Notay M, Burney WA, Sandhu S, Sivamani RK. The Skin and Gut Microbiome and Its Role in Common Dermatologic Conditions. Microorganisms. 2019 Nov 11;7(11):550.