2) YOUR SKIN IS YOUR ARMOUR - microbes & dysbiosis

1.2) Microbes

This complex and beautiful biological suit of armour is absolutely crawling with trillions of microbes (bacteria, fungi, viruses etc), passed down to us from our mother and picked up along the way. Most of our skin microbes are commensals - tiny organisms living in harmony with us. It is increasingly accepted that the key to achieving and maintaining excellent skin health lies with the health and diversity of the skin microbiome.¹

Like us, microbes eat to survive, and as they break down their food (our skin secretions), they release metabolites which impact skin health:

• Lipophilic commensals such as Cutibacterium acnes ingest sebum from sebaceous glands and releases free fatty acid metabolites⁶ which help maintain skin barrier homeostasis.¹

• Commensals such as Staphylococcus epidermidis hydrolyses the fatty acids in sebum to produce AMPs which are important immune regulators.^1,6,7

• Microbes can metabolise organic acids in order to maintain a skin pH which is hostile to pathogens.¹

• Many microbes can feed on external lipid sources such as tallow, plant oils and beeswax,¹ for example Malassezia yeast microbes in sebaceous areas of skin (they are normal commensals in healthy skin, but can cause issues if their populations grow unchecked - this will be familiar to any owner of a dog with pungent, itchy ears).

Microbes train the immune system to respond appropriately to pathogens.¹

Microbes can provide UV protection via gene expression modulation.¹

1.3) Dysbiosis

1.3a) What is dysbiosis?

When you are in a state of balance - homeostasis - the various species of microbes inhabiting your body are present in the right places and in the right numbers. Microbes are often location specific - your armpit houses totally different demographics to your foot.¹ There are dry deserts (your arm), moist rainforests (your underarm) and sebaceous oil fields (your scalp).⁶

Changes to your microbial makeup are not always harmful (dysbiotic). Improvements to diet and lifestyle can shift populations in benign or beneficial directions. Our commensal bugs can respond and change in the most unexpected ways, for example studies have shown that over time dogs and their owners develop increasingly similar microbiomes.⁸

Dysbiosis occurs when something knocks our microbes out of balance. Commensal microbes go rogue and cause harm either by invading spaces where they ought not to be, or by undergoing excessive population growth.¹

Dysbiosis can cause harm wherever it happens, which is probably a large part of the reason that many health conditions go hand and hand. For example psychiatric and psychosocial illnesses correlate with poor skin health.⁵ There may be some aspect of ‘chicken and egg’ going on here too. Severe acne could conceivably lead to depression in a vulnerable teen. And depression could lead to behaviours conducive to the development of acne. But if something has significantly damaged your microbiome in one area, then other areas of your microbiome may be at risk too, and this could result in a variety of different health conditions emerging in an individual.

1.3b) What causes dysbiosis?

It has been estimated that we have lost as much as a third of the diversity of our skin microbiome due to an ever-growing list of modern selection pressures, including:⁷

• Daily exposure to chlorinated/fluorinated water

• Preservative-containing cosmetics and foods

• Pesticides and herbicides

• High pH soaps

• C-sections

• Antibiotics

• Stress

• Pathogens

• Poor diet

• Aging⁷

Dysbiosis is to a large extent a disease of modernity. Eczema and acne ware assumed to have been rare in hunter-gatherer societies, but have dramatically increased over the last 50 years.⁷

1.3c) What does dysbiosis lead to?

Dysbiosis is probably involved (either as a cause or a consequence or both) in many instances of poor health. Disease can disrupt the microbiome, while microbial imbalance can in turn contribute to further disease, creating a self-reinforcing cycle.

Cutaneous dysbiosis leads to dryness (because reduced microbial diversity impairs barrier function which results in increased trans-epidermal water loss⁵), inflammation, pruritus (itching), infection and premature skin aging.¹

It is related to a raft of skin conditions including acne (Cutibacterium acnes is a normal commensal of healthy skin, but when there is diversity loss among the different strains of C. acnes acne vulgaris occurs⁵), psoriasis, rosacea, atopy/eczema, dandruff and body odour.^1,6,5,4

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