The Skin Microbiome: How It Protects Your Body and How Soap Can Disrupt It

When most people think about protecting their skin, they think about keeping it clean. But healthy skin is not sterile—and trying to make it so may work against one of the body’s natural protective systems.

Your skin is home to a vast community of bacteria, fungi, viruses and other microorganisms collectively known as the skin microbiome. Far from simply living on us, many of these organisms interact with the skin barrier and immune system in ways that help maintain healthy skin and protect against potentially harmful microbes. Research increasingly describes the skin not as an inert covering, but as a complex biological ecosystem and an active interface between the body and the outside world.

Your skin is a living ecosystem that helps protect your body, support immunity, and maintain a healthy barrier.

How extensive is the skin microbiome?

The skin of an average adult covers roughly two square meters, or about 20 square feet, creating an enormous habitat for microorganisms. Researchers have identified a remarkably diverse collection of microorganisms associated with human skin.

But there isn't one single skin microbiome covering your entire body.

Different areas create different microbial neighborhoods. Sebaceous, or oily, areas such as the face, chest and upper back support different microbial communities from moist areas such as the armpits and skin folds. Dry areas, including portions of the arms and hands, have their own characteristic communities and can display particularly high microbial diversity.

Microorganisms aren't necessarily limited to what we think of as the skin's exterior surface, either. Research examining skin more deeply has found microbial communities within different skin compartments, while follicles and glands provide additional specialized microbial habitats.

In other words, the skin microbiome is better thought of as a collection of interconnected ecosystems.

How does the skin microbiome protect the body?

Healthy skin defense involves several systems working together: the physical skin barrier, chemical environment, immune system and microbiome.

One important mechanism is called colonization resistance. Resident microorganisms occupy ecological niches and use resources that might otherwise be available to invading organisms. Certain skin microbes can also produce substances that inhibit other microorganisms or alter their behavior.

The microbiome also interacts extensively with the immune system.

Research indicates that resident microbes help educate and regulate both innate and adaptive immune responses. This ongoing conversation between microbes, skin cells and immune cells contributes to maintaining the skin barrier and responding appropriately to challenges such as infection or injury.

This helps explain why “bacteria” should not automatically be equated with “bad.” Many organisms normally living on healthy skin are harmless or potentially beneficial. Even organisms capable of causing problems under certain circumstances may coexist normally with us when the skin ecosystem and immune defenses are balanced.

The acid mantle: another important part of skin protection

Healthy skin maintains a naturally acidic environment commonly referred to as the acid mantle.

This acidic environment is not incidental. Skin pH contributes to epidermal barrier integrity and helps regulate the microbiome and inflammation. Alterations in pH can affect barrier properties and the conditions under which different microorganisms thrive.

Sebum, sweat, skin lipids and other components all contribute to the skin's chemical environment. The result is a surface that is relatively dry, acidic and nutrient-poor—conditions that help make healthy skin challenging territory for many potential pathogens.

Could soap interfere with the skin microbiome?

This is where our modern obsession with being “squeaky clean” deserves some perspective.

Soap doesn't distinguish between something we want removed and components of the skin ecosystem we would prefer to preserve. Cleansing products rely largely on surfactants, which help water remove oils, dirt and other material from the skin.

Traditional soaps tend to be alkaline. Research on cleansers has found that soap-based products can alter skin pH, dissolve lipids and disrupt aspects of the skin barrier, whereas appropriately formulated synthetic cleansers, often called syndets, can be less disruptive.

That does not mean soap is inherently harmful or that people should stop washing. Handwashing and appropriate hygiene remain important tools for preventing infection.

The more useful question is: How much cleansing does our skin actually need, and what are we cleansing it with?

What about lotions, cosmetics and other skin products?

Products applied to the skin can potentially influence its environment through ingredients that affect moisture, oils, pH and the physical barrier. Hygiene practices are also among the environmental factors associated with differences in skin microbial communities.

However, it would be an oversimplification to say that all cosmetics or skin-care products damage the microbiome. Some studies have found that particular lotions can improve hydration without substantially changing certain common commensal organisms.

The effects depend on the formulation, ingredients, frequency of use, body location and the individual's skin.

Products of particular interest include strong surfactants, highly alkaline soaps and products used very frequently. Preservatives, fragrances and other ingredients may also matter for individual skin tolerance, but their presence does not automatically mean that a product damages the microbiome.

Are we over-cleaning our skin?

For decades, personal-care marketing has often equated cleanliness with removing oil, bacteria and odor as thoroughly as possible. Microbiome research provides a more nuanced picture.

The goal of healthy skin care should not be to sterilize the skin. That is neither realistic nor desirable.

Instead, it may be more helpful to preserve the conditions that allow the skin barrier and its resident microbial ecosystem to function normally.

For everyday skin care, that generally means avoiding unnecessary aggressive cleansing, paying attention to how your skin responds to products, and considering gentle cleansers when frequent washing is necessary. People with eczema, dermatitis, infections or other skin conditions should discuss their cleansing and skin-care routine with a dermatologist rather than attempting to manipulate the microbiome themselves.

Your skin is more than a covering

Perhaps the most important shift emerging from microbiome science is conceptual.

Your skin isn't simply a wall separating you from the environment. It is a living interface connecting your environment, your microbiome, your immune system and your body.

Every square inch supports an intricate biological relationship that science is still working to understand.

So the next time you wash, scrub, disinfect or apply a product to your skin, remember: you're not caring for an empty surface.

You're caring for an ecosystem.

References & further reading

For readers who want to explore the science, excellent starting points include the Nature Reviews Microbiology overview of the human skin microbiome, the PubMed review on the skin acid mantle and pH, the PubMed review on skin microbiota and barrier function, and the review comparing soaps and synthetic cleansers.