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Questions and answers about the skin microbiome and pre- and probiotics.

We, humans, and the many bacteria that live in us and on us have evolved together for millennia. This stuff may sound yucky but what is actually is yucky it’s when the bacteria are not there. Our body needs them, they are crucial to the immune system and epidermal development and differentiation.

Microbe colonization of our skin is no longer perceived as a threat but as a factor to be evaluated depending on the circumstances.

Bacteria are so enmeshed with the human body that, for some purposes, they could be considered part of it. This relationship starts as soon as a baby makes its way through the birth canal, collecting bacteria, viruses, and mold as the baby comes out.

These days the term microbiome has replaced the older term, bacterial flora. Same thing. Because the microbiome is so important to our health, I want to discuss the bacteria associated with the skin. The skin microbiome is the complex community of bacteria, viruses, and fungus that live in and on our skin. Most of the microbiome, most of the time, is useful and necessary. Most of the time: I don’t like the after-gym odor either.

Kill the bacteria? Not so fast!

The practice of using non-specific antimicrobials to fight skin bacterial communities is now being reconsidered. Why? They also affect beneficial, commensal species.

Which organisms make up the natural skin microbiome?
In healthy skin, you will find Cutibacterium acnes (formerly Propionibacterium acnes), Staphylococcus epidermidis, and Corynebacterium, plus others present at lower concentrations.

What do these bacteria do for us? They discourage other (potentially dangerous for us, competition for them) microorganisms from invading our skin by making it unsuitable for the invaders.

The same bacterial species can be an enemy one day and a friend the next. An example of the commensal–pathogenic bacteria duality: two species, Staphylococcus epidermidis and Cutibacterium acnes have been suggested as acne-causing agents and as resident bacteria that inhibit pathogenic bacteria growth and decrease the risk of disease development. Complicated, right? Part of the problem is that the “old” classification of bacterial species did not take into account specific genetic markers that can confer extra aggressivity and the capacity to disrupt skin physiology.

In general, the skin microbiome is best left alone unless its disruption becomes apparent, like with acne.

PRO. What are probiotics?

The official definition is this: “live microorganisms which when administered in adequate amounts confer a health benefit on the host”. A probiotic is a mix of live bacteria and/or yeast that are ingested to improve the health of the digestive system. A common use of probiotics is when we use them after taking an antibiotic, to compensate for the disruption of the natural digestive flora.

Why can’t you buy probiotics for the skin?

The FDA (Food and Drug Administration in the USA) sets strict limits for the number of live bacteria present in cosmetics and skincare products. This makes sense: we must avoid excess or dangerous bacteria from entering our bodies, and anything you apply on the skin can potentially enter the body.

Our digestive system, with a stomach at a very low pH, is well equipped to kill bacteria. Conversely, our skin is not well equipped to kill dangerous bacteria and, in the old times (as I always say, the old times were not better) without preservatives, contaminating bacteria present in cosmetics caused terrible damage, including blindness.

What about DIY probiotics?

You shouldn’t play with fire, but if you make yourself a plain yogurt mask using plain, full-fat yogurt, it may leave behind some beneficial Lactobacillus, which may help control S. aureus infections, atopic dermatitis, and acne.

PRE. What is a prebiotic?

Prebiotics are chemical components in food that induce the growth or activity of beneficial microorganisms. The most common example is the gastrointestinal tract, where prebiotics like natural food fibers can change for the better the composition of the gut microbiome.

For the skin, some strains of S. epidermidis can ferment carbohydrates to produce succinic acid, a chemical that has potent anti-S. aureus and anti-C. acnes activity. This is relevant to acne treatment because, in theory, we could improve skin health by using prebiotics like succinic acid and glycerol that will discourage C. acnes from spreading.

We can’t use topical probiotics (live bacteria) on our skin for very good reasons, but we can use prebiotics, and we already do! The ingredients in Skin Actives Scientific acne control products contain several chemicals that modify the skin environment to make it less hospitable to acne bacteria. We will continue to add more prebiotics to improve our products as we learn more about the skin microbiome.

It seems that a change in the skin environment is essential for the development of acne. Conversely, a different change in the environment should help control this condition. We prefer discouraging the bad bacteria, rather than killing all bacteria as benzoyl peroxide would do.

How does skincare affect the skin microbiome?

The acne bacteria break down triglycerides present in sebum and use the fatty acids as a nutrient source. Creams and lotions promote skin hydration, resulting in a drop in sebum content, which could decrease the abundance of acne bacteria.

For better (and for worse)

Not all actives are good for everything. Vitamin B12 supplementation was found to induce porphyrin production in C. acnes strains from acne patients, whereas the C. acnes strains from healthy people did not have this ability.  Porphyrin can induce skin inflammation and acne development, so vitamin B12 supplementation in association with C. acnes may worsen acne.

Do you need to stop bathing to protect your microbiome?

No, just like you don’t need to stop brushing your teeth to protect the bacteria that reside in your mouth (yes, yucky). And you can use deodorant. You don’t need to “go natural” and discourage people from approaching you in order to protect your health.

Do you need to spray “live” bacteria on your body?

No. And the law does not permit the sale of skin products containing live bacteria. Whatever the advertising says, there is a strict limit of how many live bacteria are allowed in a skincare product. If a brand is trying to sell you a product with live bacteria capable of growing on your skin, they are lying.

Sensitive skin and microbiome

Cause and effect are important here. Some “skincare” products are likely to kill bacteria and modify the microbiome. One consequence may be sensitive skin. In a group pf people who complained of having sensitive skin, Lactobacillus and Mucor racemosus were more abundant, and Malassezia restricta was less abundant. Some “skincare” products, like those containing alcohol, acid peels, detergents, or oxidants, may be a cause of sensitive skin.

Cause or consequence?

Inflammatory skin diseases are associated with an imbalance of the skin microbiome. Studies have demonstrated specific pathogens to be associated with each specific disease. This does not mean causality, it may be simply that bacterial populations change as a result of skin physiological changes. One notable example: adolescents produce more sebum, leading to acne. The use of “natural” antiperspirants will increase pH and encourage fungal growth.

Take-home lesson

Don’t attack what you don’t know: if you start using strong oxidants like benzoyl peroxide or anti-bacterial products, or remove the external layers of the epidermis that constitute the natural skin barrier, you may get into trouble because you will be disrupting the natural equilibrium achieved by the skin and its microbiome.

Strong detergents in the shampoo will do the same kind of damage to the scalp.

Don’t feed “bad bacteria” with coconut oil and similar fats.

Don’t use “natural” anti-antiperspirants that increase the natural, acidic pH of the skin, it will encourage the growth of fungi and you will have to deal with a nasty infection.

No strong oxidants (like benzoyl peroxide)

No ethanol, denatured alcohol, or strong solvents

Keep skin pH on the acidic side

Shower after the pool, otherwise the leftover chlorine, a strong oxidant, will damage your skin and your microbiota

How much should you worry about the skin microbiome?

Worrying is bad for us. I would not worry unless an actual problem arises. Don’t listen to all that talk about natural, keep taking your showers and washing your hair.

How can we, at Skin Actives, help you protect your skin’s microbiome? We respect skin physiology and our products are designed to protect your skin and heal it. They will also protect your skin microbiome.


Wilmanski, T., Diener, C., Rappaport, N. et al. Gut microbiome pattern reflects healthy ageing and predicts survival in humans. Nat Metab 3, 274–286 (2021).

Moskovicz, V., Gross, A., & Mizrahi, B. (2020). Extrinsic Factors Shaping the Skin Microbiome. Microorganisms, 8(7), 1023. doi:10.3390/microorganisms8071023 

Nørreslet, L. B., Agner, T., & Clausen, M.-L. (2020). The Skin Microbiome in Inflammatory Skin Diseases. Current Dermatology Reports. doi:10.1007/s13671-020-00297-z 

Keum, H. L., Kim, H., Kim, H.-J., Park, T., Kim, S., An, S., & Sul, W. J. (2020). Structures of the Skin Microbiome and Mycobiome Depending on Skin Sensitivity. Microorganisms, 8(7), 1032. doi:10.3390/microorganisms8071032