The Deep-Dive Series: The Skin Microbiome

The skin is the human body’s largest organ. It has its own ecosystem, made up of a diverse milieu of microorganisms that are together called ‘the skin microbiome’.

These bacteria are part of the 100 trillion microbes living in and on us- that’s 10 single-celled organisms for every human cell in the body! Whether the notion of it frightens or fascinates us, these organisms are fundamental components of our physiology. Called ‘commensal organisms’, they share a long-term, symbiotic relationship with us, protecting us from pathogens and even boosting our own immune system.

Let’s take a deep dive into the composition and helpful effects of the skin microbiome.


The Types of Microbes that Live on our Skin

Apart from bacteria, our skin also contains fungi, viruses, mites and – the most recently discovered – archaea, which are microbes that love extreme environments and are found more commonly on people who have dry skin. The microbes that live on a person are a unique reflection of his/her age, sex, genetics, diet, lifestyle, habits and location.

Our skin gets colonised by microorganisms the minute we’re born. This initial flora isn’t diverse and resembles that of our birth site: a vaginal birth will mean the new-born’s skin is colonised by vaginal flora, while a caesarean section birth will result in flora typical of stomach skin. Either way, this initial colonisation is imperative to our immunity being built against microorganisms.

As we mature from infancy to adulthood, physiologic changes in the skin lead to significant shifts in the microbiota. During adolescence, our sebaceous glands are stimulated by hormones and increase in activity – the microbiota is now dominated by oil-loving bacteria. Ageing, on the other hand, is characterised by a decrease in sweat, sebum and immune functions, changing the ecosystem once again.

Even the microbiota on a single person’s skin at a given time varies across different types of areas, the main ones being areas rich in sebum, moist areas and dry surfaces. For instance, sebaceous areas are largely occupied by a genus that includes P. acnes, which is associated with acne when in high numbers. Moist areas, on the other hand, are frequented by odour-producing bacteria, which create the odour associated with our sweat.


Functions of the Skin Microbiome

Protecting us from pathogens

There are a few ways in which our skin’s microbiome protect us from potentially infectious organisms:

1] They compete with pathogens for space and nutrients

By residing on our skin, the commensal (symbiotic) microorganisms take up nutrients and space, limiting the potential for pathogens to grow when they’re introduced to the skin’s surface.

2] They produce antimicrobial compounds

A large number of bacteria are known to directly restrict the growth of competitors by producing antimicrobial compounds. These compounds affect other species of bacteria, serving as defence mechanisms and preventing their growth.

For instance, S. aureus is a bacteria commonly linked to atopic dermatitis, and infects our skin, producing boils, redness, swelling and oozing layers. There are two type of bacteria that reside on our skin and protect us from S. aureus. Called S. epidermidis and S. homonis, these bacteria have been shown to decrease the colonisation of S.aureus and of atopic dermatitis when their numbers are repopulated on our skin.

Some bacteria even convert ‘nitrate’, a compound found in our sweat, to ‘nitrite’ – this compound forms free radicals, which then exhibit antibacterial and antifungal defence mechanisms.

3] They create environments unsuitable to pathogenic growth

The bacteria that live on our skin prefer of a pH of around 5, which is quite acidic. The skin’s first line of defence is the acid mantle, which is a thin film on our skin that’s created by bacteria after digesting the sebum on our skin.

P.acnes use sebum as an energy source, which leads to the release of free fatty acids. This action also creates a pH of 5.5 for the acid mantle, which inhibits the growth of certain harmful bacteria.

Triggering our immune system

The skin is an imperative part of our immune system. Its immune response helps us heal wounds, fight infections and it even regulates the type of microbes that live on our skin.

The commensal bacteria on our skin can identify potential pathogens. Upon doing so, they secrete compounds that trigger our skin’s immune system into launching a defence against the invading microorganisms.


The ‘Dysbiosis’ of the Skin Microbiome

Seeing how our skin and its microbiome work together, it’s easy to see why our skin is commonly thought of as a shield that prevents external factors from harming us.

To do so requires a balance between our skin’s environment, the populations of commensal microbiota and the numbers of potentially harmful micoorganisms.

When this equilibrium is disrupted, it leads to ‘dysbiosis’ – a change in the abundance and diversity of commensal species, which can aggravate chronic skin diseases like atopic dermatitis, psoriasis or acne.

For instance, dandruff can be caused by dry skin or infection. If the latter is the cause, that would indicate a disequilibrium between the bacteria and commensal fungi on our scalp.


Triggers that Cause Dysbiosis

1) The skin products we use (cosmetics, soaps, hygienic products and moisturisers) we use can alter our skin microbiome. Soap, by nature, is alkalinising. A more alkaline pH is preferred by the skin’s harmful bacteria, whereas the healthy microbiome thrive at a relatively acidic pH of about 5. Even alcohol-based skin applications like toners or cologne could change our skin’s microbiome composition and make us vulnerable to pathogens.


How to address this:

Using soap-free and alcohol-free products on our skin can help maintain the balance of our skin’s ecosystem.

2) The sun’s UV rays (specifically UVR rays) have been reported to kill bacteria, as these rays can over-activate our immune system.


How to address this:
Applying sunscreen and eating foods rich in antioxidants (especially carotenoids) and vitamins E and C can help protect us from UV-R rays.


3) Consuming alcohol has been linked (by mounting evidence) to changes in our microbial composition of our skin, gut, oral cavity and other mucous-containing surfaces. Given that this would impair our immune system, it explains why people who drink frequently and excessively have a higher frequency of bacterial and fungal skin infections.


How to address this:
Drinking alcohol in moderation can help reduce these alterations in our microbiome.


4) Antibiotics were – and still are – a milestone that changed the way we treat bacterial infections. However, their overuse today has become a general health issue, making strains of pathogenic microorganism resistant to their effects while also killing both the good and the bad species of microbes.


How to address this:

Consuming probiotics (like yoghurt) and consuming oral probiotic formulations specifically for the skin can help restore the skin’s microbiome. A new generation of emollients and moisturisers now contain probiotic formulations, which can also be useful especially while managing skin diseases like atopic dermatitis and acne.

In addition to oral probiotics formulations developed for the skin, a new generation of emollients and moisturizers now include probiotic formulations, designed to support the management of skin diseases such as atopic dermatitis or acne.


5) Hormonal imbalances (during puberty, PCOS, pregnancy, as examples) can cause excess sebum overproduction, which encourages the overgrowth of P. acnes, thus leading to acne and dysbiosis. Similar hormonal imbalances are also seen in conditions like PCOS, pregnancy and menopause.


How to address this:

Addressing the cause itself, i.e., the hormonal imbalance, would be the most effective way to restore the skin’s balance. Exercising regularly and eating a balanced diet can go a long way, and a medical professional may even recommend hormone therapy.


6) Anti-inflammatory medicines (both oral or topical) are used to treat skin conditions like atopic dermatitis and psoriasis. However, these can alter our hormones, immune response and skin environment to the extent of dysbiosis, and worsen the issue.


How to address this:

If you’re on anti-inflammatory medicines for skin conditions that aren’t improving, it would be best to speak to a medical professional and find suitable solutions.


7) The relationship between our gut and skin microbiome is still under study, but experts firmly believe that our skin’s physiology can be affected by our gut bacteria.

Even the bacteria in the gut prevent toxins from passing into our bloodstream. When there are fewer numbers of these good bacteria, toxins are able to enter the bloodstream and reach the skin, disrupting its environment and causing dysbiosis.


How to address this:

Although much is yet to be understood the way nutrients directly affect our skin’s microbiome, it’s fair to say that eating foods that improve our gut health will our skin’s microbiome’s stay healthy, too.

Foods rich in prebiotics (fibre-rich fruits, vegetables and whole grains), probiotics (which are fermented foods like curd, kombucha and kefir) and DHA (foods like fatty fish, marine algae) help populate our gut with good bacteria and maintain its health.



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