The Microbiome: Understanding the Ecosystem Within

For decades, skincare focused on what needed to be removed from the skin.

Today, we know that healthy skin depends not only on the cells that make up the ski barrier, but also on the trillions of microorganisms that live alongside it.

Collectively known as the skin microbiome, this complex ecosystem plays a critical role in barrier integrity, immune regulation and inflammation. The health of the skin is closely linked to the health of this microbial community.

At SIHA, understanding the microbiome is not about eliminating bacteria. It is about supporting the conditions that allow
balance to thrive.

What Is the Microbiome?

A microbiome is defined as a community of microorganisms that inhabit a specific environment within the body.

We do not have a single microbiome. We have many.

There is a gut microbiome, oral microbiome, skin microbiome and, in women, a vaginal microbiome. Each occupies its own unique niche and performs specialised functions that contribute to overall health.

While each microbiome operates differently, they are deeply interconnected through immune, inflammatory and metabolic pathways. A disruption in one area of the body can often be reflected elsewhere — including the skin.

The Gut Microbiome: The Foundation of Immune Health

The gut microbiome is the largest and most extensively studied microbial ecosystem in the body.

Containing trillions of microorganisms — including bacteria, viruses and fungi — the gut plays a vital role in digestion, nutrient absorption, metabolism and immune regulation.

In fact, approximately 70–80% of the body's immune cells reside within the gut-associated lymphoid tissue.

One of the gut microbiome's most important functions is educating the immune system. Beneficial microorganisms help immune cells distinguish between harmless organisms and genuine threats, reducing unnecessary inflammatory responses. 

When this ecosystem becomes imbalanced, a state known as dysbiosis, the effects can extend far beyond digestion. Digestive discomfort, bloating, constipation, diarrhoea, poor nutrient absorption and food sensitivities are common signs. However, dysbiosis may also contribute to systemic inflammation, immune dysregulation and skin conditions
such as acne, rosacea and dermatitis.

This relationship is often referred to as the gut-skin axis. What happens within the gut rarely stays within the gut.

The Oral Microbiome: The Gateway to the Body

The mouth contains one of the most diverse microbial communities in the body. The oral microbiome assists with digestion, nutrient release and immune regulation, while also acting as an important protective barrier against pathogens - yet it is often overlooked.

Many conventional oral care products are designed to eliminate bacteria indiscriminately. While antibacterial mouthwashes may reduce harmful bacteria, they can also disrupt beneficial microbial species that contribute to balance and resilience.

When the oral microbiome becomes compromised, pathogens may gain easier access to the bloodstream and circulate throughout the body. Research continues to explore links between oral dysbiosis and a range of chronic health conditions, including cardiovascular disease, diabetes, pneumonia and certain cancers.

The lesson is one that appears repeatedly throughout microbiome science: health is supported by microbial diversity, not microbial elimination.

The Vaginal Microbiome: A Protective Ecosystem

The vaginal microbiome is a dynamic ecosystem predominantly populated by Lactobacillus species. These beneficial bacteria help maintain a naturally acidic environment that discourages the growth of pathogens and opportunistic organisms.

This low pH acts as a protective barrier, helping to maintain microbial balance and support overall vaginal health. Like every microbiome within the body, stability and diversity are more important than sterility.

The Skin Microbiome: An Invisible Layer of Protection

The skin is home to billions of microorganisms.

For decades these organisms were viewed primarily as contaminants. Today, we understand they form an essential component of healthy skin function. One of the most useful ways to think about the skin microbiome is as a garden.

In a thriving garden, healthy soil supports beneficial plants while naturally limiting the growth of weeds. When the soil becomes depleted, overworked or damaged, opportunistic species begin to dominate. The same principle applies to the skin. Healthy skin is not skin without bacteria. Dysbiosis is not simply the presence of harmful microorganisms. It is often a sign that the environment no longer supports balance.

When beneficial microorganisms are evenly distributed across the skin, there is little opportunity for pathogenic species to establish themselves. When imbalance occurs,
inflammation often follows.

This may present as:

• Acne
• Rosacea
• Dermatitis
• Sensitivity
• Impaired barrier function
• Premature skin ageing

Often, the issue is not what is present. It is what is missing.

Why pH Matters

The skin naturally maintains a slightly acidic pH, generally between 4.5 and 5.5. This acidic environment supports beneficial microbial populations while suppressing pathogenic growth.

When pH is altered through aggressive cleansing, excessive exfoliation, overuse of active ingredients or poorly balanced formulations, the consequences extend beyond the
barrier itself.

We do not simply disrupt the acid mantle. We also alter microbial signalling and communication. The skin's protective ecosystem can shift rapidly from a balanced and resilient environment into a reactive one. This is one reason why barrier impairment and microbiome imbalance are so often seen together.

Beyond Skincare: Lifestyle and the Microbiome

The microbiome is shaped not only by what we apply to the skin, but also by how we live.

Diet, stress, sleep quality, environmental exposures, medications and antibiotic use can all influence microbial diversity throughout the body.

Chronic stress, for example, has been shown to influence both gut and skin microbial populations while also impairing barrier function and increasing inflammation. Similarly, poor dietary diversity may reduce microbial diversity within the gut, affecting immune regulation and potentially contributing to inflammatory skin conditions.

Supporting the microbiome therefore extends beyond skincare, it is a whole-body conversation.

Prebiotics, Probiotics and Postbiotics

As microbiome science has entered the skincare industry, terms such as prebiotic, probiotic and postbiotic have become increasingly common. Understanding the difference is important.

Prebiotics

Prebiotics act as a food source for beneficial microorganisms. In skincare formulations they may appear as specialised sugars, fibres or plant-derived compounds that help create an environment supportive of microbial diversity.

However, prebiotics cannot perform their intended role if the formulation simultaneously contains harsh ingredients including fragrances and preservatives that disrupt microbial balance.

Probiotics

Probiotics are live microorganisms. While live probiotics are valuable within the gut, incorporating them into skincare is significantly more challenging.

Skincare products must remain stable and safe throughout their shelf life. Encouraging live microbial growth within a formulation creates obvious formulation challenges.

For this reason, many products marketed as probiotic skincare contain probiotic-derived ingredients rather than live cultures.

Postbiotics

Postbiotics are the beneficial compounds produced when microorganisms metabolise nutrients. In simple terms, they are the functional outcome of microbial activity.

These bioactive compounds can help:

• Strengthen barrier integrity
• Support hydration
• Optimise skin pH
• Moderate inflammation
• Improve skin resilience

Unlike live probiotics, postbiotics offer a stable and predictable way to support microbial health through skincare. In many respects, they represent the intelligence of the microbiome delivered directly to the skin.

Restoring Conditions, Not Controlling Outcomes

One of the principles of corneotherapy is that healthy skin is capable of maintaining itself when the right conditions exist. Rather than attempting to force change through aggressive treatments or excessive intervention, corneotherapy focuses on restoring barrier integrity, reducing inflammation and supporting the skin's natural regulatory systems.

The microbiome is one of those systems.

When the barrier is intact, hydration levels are maintained, lipid composition is balanced and pH remains slightly acidic, beneficial microorganisms are naturally supported. In many cases, dysbiosis is not the primary problem but a consequence
of a disrupted skin environment.

This is why barrier impairment and microbiome imbalance are so often seen together.
When we support the skin's structure and function, we also support the microbial communities that depend on it.

The goal is not to control the microbiome. The goal is to create the conditions in which balance can return.

To summarise:

• Healthy skin is not sterile skin. Beneficial microorganisms are an essential part of skin function.
• The skin microbiome is closely connected to the gut, oral and vaginal microbiomes through immune and inflammatory pathways. 
• Dysbiosis is often a sign that the environment no longer supports balance.
• The skin's naturally acidic pH helps support beneficial microbial populations and discourage pathogenic growth.
• Over-cleansing, excessive exfoliation and aggressive active ingredients can disrupt both the barrier and the microbiome.
• Supporting the skin barrier is one of the most effective ways to support a healthy microbiome.
• Postbiotics offer one of the most stable and evidence-based ways to support microbial balance through skincare.
• Diversity matters. The goal is not to eliminate microorganisms, but to encourage a resilient and balanced ecosystem.