We tend to think of the immune system as something happening deep inside us, an invisable army stationed somewhere behind the ribcage. But a large part of its daily regulation actually happens right at the surface: on your skin, in your mouth, along your gut.
The skin, oral cavity, and gut are not just physical barriers, but complex ecosystems populated by trillions of microorganisms that continuously communicate with our immune system.
These microbial communities (our microbiomes) are increasingly recognised as essential regulators of immune balance, inflammation, and barrier function. Importantly, they are highly sensitive to the environment we expose them to, including the personal care products we use every day.
The body as an ecosystem
The human body hosts separate but interconnected microbial ecosystems:
- Gut microbiome: central to immune education, metabolic regulation, and inflammatory balance
- Skin microbiome: acts as a protective border against pathogens and environmental stressors
- Oral microbiome: influences local inflammation and has systemic links to immune function
The skin alone is a dynamic immune organ, constantly interacting with microbes and environmental factors, helping regulate immune responses and barrier integrity. Similarly, the skin microbiome is not passive, it actively supports immune homeostasis and protects against pathogen overgrowth 1,2.
Why the microbiome matters for immunity
Across all these ecosystems, microbes play several key roles:
- Training and modulating immune responses
- Producing metabolites (byproducts) that influence inflammation
- Strengthening the body's lining to block harmful substances while still letting important nutrients pass through.
- Preventing colonisation by harmful organisms
For example, skin commensal bacteria (the beneficial microbes that naturally live on us) can produce metabolites that strengthen barrier integrity and support immune signalling pathways. This means the microbiome is not separate from immunity, it is part of how immunity is regulated every day 3 .
Personal care products: a constant environmental exposure
Unlike diet or lifestyle factors that vary, personal care products are applied daily and directly onto microbiome-rich surfaces.
These include:
- Shampoo and shower gels
- Moisturisers and lotions
- Deodorants and antiperspirants
- Toothpaste and mouthwash
- Cleansers and soaps
Because these products are used repeatedly and over long periods, even subtle effects on microbial ecosystems may accumulate. Research shows that personal care products can alter both the chemical environment of the skin and its microbial diversity, sometimes with changes lasting days to weeks after use 4.
Key chemicals in conventional personal care products
Many conventional formulations contain ingredients designed to clean, preserve, fragrance, or alter microbial growth. Some of the most common include:
1. Antibacterial agents
- Triclosan (restricted in many regions but historically widely used)
- Benzalkonium chloride
These are designed to reduce bacterial load but may also affect beneficial microbes and contribute to microbial imbalance.
2. Preservatives
- Parabens (e.g., methylparaben, propylparaben)
- Phenoxyethanol
- Isothiazolinones (e.g., methylisothiazolinone)
Preservatives prevent microbial contamination of products, but their broad antimicrobial activity can also influence skin microbial communities 5.
3. Surfactants and detergents
- Sodium Lauryl Sulfate (SLS)
- Sodium Laureth Sulfate (SLES)
These are cleansing agents that remove oils and microbes but can also disrupt the skin barrier when used excessively.
4. Fragrances and solvents
- Synthetic fragrance compounds
- Alcohols (e.g., ethanol, isopropanol)
These can contribute to irritation or barrier disruption in sensitive individuals.
5. Deodorant-specific ingredients
- Aluminium salts (antiperspirants)
- Antimicrobial compounds
- Fragrance systems
Studies suggest deodorants may alter underarm microbial composition by selectively suppressing certain bacterial groups while allowing others to dominate 4.
How these ingredients can influence the microbiome
The microbiome is shaped by a balance of nutrients, moisture, pH, and microbial competition. Personal care products can alter these conditions by:
1. Reducing microbial diversity - Harsh antimicrobial or detergent-based products may reduce both harmful and beneficial microbes, potentially decreasing ecosystem stability.
2. Shifting microbial balance (dysbiosis) - Selective suppression of certain species can allow others to dominate, changing the overall microbial community structure.
3. Altering skin barrier function - Some ingredients can disrupt the lipid (fat) barrier, increasing sensitivity and inflammatory potential.
4. Changing skin chemistry - pH shifts and residue from products can influence which microbes survive on the skin surface 4,6.
And it turns out these effects don't stop at the skin's surface...
The Gut-Skin-Immune Axis
Emerging research highlights that the gut and skin are not separate systems but part of a connected immune network. Disruption in one microbiome may influence systemic inflammation and immune regulation via this “gut–skin axis.” This reinforces the idea that skin health is not only topical, but also systemic 1,7.
The same logic applies closer to home - in your mouth, twice a day every day.
The Mouth–Immune Axis
The oral cavity is one of the most microbially active environments in the body, home to hundreds of different microbial species. The oral microbiome plays an important role in immune function, acting as a key communication point between the outside world and our internal systems.
Because the mouth is constantly exposed to food, air, and environmental factors, it acts as an important immune checkpoint. The microbes living there help regulate inflammation, support the health of the mouth’s lining, and communicate with the immune system. When this balance is disrupted (known as oral dysbiosis), it may contribute to higher levels of inflammation in the body overall 8,9.
Questioning everyday toothpaste
Toothpaste is one of the most frequently used personal care products. Yet, many conventional formulations contain ingredients that go beyond simple cleaning and may actively influence the oral environment.
Common ingredients include:
- Foaming agents such as sodium lauryl sulfate (SLS), which can affect mucosal surfaces in sensitive individuals
- Artificial sweeteners and flavouring agents
- Strong antimicrobial compounds in some formulations
- Abrasives designed to mechanically remove plaque
While these ingredients are not inherently harmful for most people, the oral microbiome literature suggests that broad antimicrobial approaches may reduce microbial diversity rather than selectively targeting harmful organisms 10.
This raises an important question: are we supporting oral balance, or simply stripping it away?
Microbiome-conscious approach to oral care
Emerging approaches to oral health are beginning to shift away from broadly antibacterial strategies toward supporting microbial balance.
This includes formulations that aim to:
- Maintain microbial diversity rather than eliminate it
- Support the natural oral environment and pH
- Work alongside the body’s existing defence systems
For example, ingredients such as hydroxyapatite (a naturally occurring mineral in teeth) have been explored for their role in supporting enamel without disrupting the oral ecosystem, while paraprobiotics (non-live microbial components) are being studied for their potential to interact with the immune system in a more targeted way 11,12.
“Pro-Bacterial” vs “Anti-Bacterial”: A shift in thinking
Traditionally, hygiene has focused on reducing microbial presence. However, modern microbiome science suggests a more nuanced approach:
- Not all bacteria are harmful
- Many are essential for immune balance
- Overuse of antimicrobial products may reduce resilience
This does not mean avoiding hygiene, but rather:
- Supporting microbial diversity
- Avoiding unnecessary antibacterial exposure
- Choosing gentler formulations where possible 13
Supporting the microbiome in daily life
Practical, evidence-aligned strategies include:
1. Choose milder cleansing products - Mild, pH-balanced cleansers are less disruptive to microbial networks than harsh detergents.
2. Reduce unnecessary antibacterial exposure - Avoid routine use of strong antibacterial agents unless medically needed.
3. Simplify product routines - Fewer overlapping products = fewer chemical interactions with microbiota.
4. Support barrier health - Ingredients that support hydration and barrier lipids help maintain microbial balance.
5. Be mindful of fragrance and additives - Especially for sensitive skin, reducing synthetic fragrance exposure may help minimise irritation 14.
Closing thoughts
The skin, oral cavity, and gut microbiomes form an integrated ecosystem that plays a central role in immune regulation. Everyday personal care products directly interact with these microbial communities, meaning that what we apply to our body is not biologically neutral.
Current evidence suggests that while hygiene is essential, excessive or harsh antimicrobial exposure may influence microbial balance and barrier function. A more modern approach is not “anti-bacterial”, but pro-microbial balance, supporting the body’s natural ecosystems rather than stripping them away.
Understanding this relationship reframes everything.
Personal care isn't only about cleanliness, it's about working with your body, not against it.
