Today, interest in the human microbiota and microbiome is no longer limited to research labs. The importance of microorganisms that live in the human body is being widely discussed in the fields of public health, drug research, skincare, and cosmetics, to name a few. However, scientific terms aren’t always used correctly in writing aimed at the general public, which creates some confusion. One of the most common questions asked when looking into the subject is: what is the difference between microbiota vs. microbiome?

Let’s look at what microbiota and microbiome are, how they differ, and their role in the human body, particularly on the skin.

The terms “microbiota” and “microbiome” are often used interchangeably, but they are not perfect synonyms. Before diving into the key differences between the two, let’s look at each term individually:

What is the Microbiota?

The microbiota is the wide variety of microorganisms that live in a certain environment: so the “human microbiota” includes all bacteria, viruses, fungi, and other single-celled organisms living in the human body. Every human body is host to anywhere between 10 trillion and 100 trillion microorganisms from over 1,000 different species. These organisms live in many different sites of the human body, such as skin, gut, mouth, lungs, and more.

What is the Microbiome?

The term “microbiome” refers to the collective genomes of the microorganisms in a given environment, meaning the collection of all their genetic material (DNA and RNA).

What is the Difference Between Microbiome and Microbiota?

To understand the difference between microbiome and microbiota, let’s create an analogy. First, picture a parking lot. Then, fill the lot with an assortment of cars of your choice. Then, add one important detail: in the trunk of every car, there is its operating manual, containing that car’s blueprint and repair instructions.

In this analogy, the cars are microorganisms, and the parking lot is the environment where they live (for example, the human skin). Collectively, all the vehicles in the parking lot make up the “microbiota”. Meanwhile, the manuals and blueprints in the trunk of each car make up the “microbiome”.

Skin is the largest organ in the human body, and home to over 10 billion bacterial cells, which is roughly one million bacteria per square centimeter of skin. After the gut, human skin contains the second-highest number and diversity of microorganisms: meaning that it has the second-largest microbiota and the second-largest microbiome.

Being the body’s first line of defense, human skin provides a physical and chemical barrier against invasion by foreign substances or microorganisms and has an elaborate immune system to fight off infection. When a symbiotic balance is maintained between the skin and its microbiota, the resident microorganisms can help both of the skin’s protective functions by:

• Helping the skin preserve its barrier functions, for example, by degrading the lipids on the skin surface;
• Promoting adaptive immune responses;
• Creating a hostile environment for foreign bacteria;
• Protecting against the immuno-suppression resulting from UV radiation; and
• Inducing expression of antimicrobial peptides.

Humans initially acquire skin microbiota from their mother during birth, and from the environment shortly after. As we age, our skin microbiome and microbiota change and adapt depending on our environment and the state of our bodies. A major change in skin microbiome and microbiota also happens during puberty, which is frequently responsible for skin problems, including acne.

It is important for a human body to maintain a balanced, symbiotic relationship between the skin and skin microbiota. Disruption of this balance can lead to inflammation, infection, allergies, and autoimmune responses.

Microbiome diversity is also important. Research shows that healthy skin plays host to a more varied collection of microorganisms. The reverse is also true: some studies link lower microbiome diversity to a higher allergic response and skin inflammation.

The balance and composition of skin microbiota and microbiome can be affected by our age, lifestyle, and medication–but also by products we put on our skin. Makeup, skincare, and hygiene products that are too aggressive can change the skin’s natural pH level and disrupt the microorganisms’ environment.

Today, consumers are increasingly aware of the importance of skin microbiota. They want products that don’t disrupt the symbiotic relationship between their skin and its indigenous bacteria–while some go further by choosing products that actively promote the balance and safety of skin microbiota. To answer this need, cosmetics and skincare product manufacturers are introducing products marketed as microbiota-friendly, prebiotic or even probiotic.

As any other product claims, microbiota-frienfly, prebiotic and probiotic claims require testing and substantiation, which can be achieved with the skin microbiota test.

The skin microbiota test uses in vitro and ex vivo models to assess the impact of compounds or formulations on the development of different bacteria on the skin. This allows manufacturers of cosmetics or dermatological products to study how the skin microbiota is affected by their products or ingredients, and provides data to substantiate microbiota-friendly, prebiotic  and probiotic claims.

The skin microbiota test analyzes the interaction between compounds and skin microbiota by evaluating, among other things:

• Biological response of 2D or 3D skin models
• Bacterial adhesion on 3D skin models
• Bacterial viability
• Bacterial load and colony count