How to help the trillions of microbes living on your skin

Key takeaways

• NIH scientists estimate that about 1 billion bacteria live on a typical square centimeter of skin, including those in hair follicles and glands².
• Oily, moist and dry areas each host their own mix of microbes, and body site matters more than whose skin it is¹.
• Friendly residents such as Staphylococcus epidermidis make natural antimicrobial compounds and help train your skin’s defenses¹⁵.
• Gentle care, such as short, warm showers and a mild, fragrance-free cleanser, respects the cool, slightly acidic surface your microbes prefer¹¹⁰.
• Probiotics, the helpful live microbes found in yogurt, fermented foods, dietary supplements and beauty products, are a fast-growing area of skin research⁹¹².

Right now, roughly 1 billion bacteria are living on each square centimeter of your skin, a patch smaller than a postage stamp. That estimate comes from researchers at the National Institutes of Health (NIH), and it includes the microbes living down inside hair follicles and glands².

An average adult has about 1.8 square meters of skin, roughly the size of a twin mattress top¹. Across that much skin, the numbers add up fast. Trillions of bacteria, fungi, viruses and even tiny mites make their homes on human skin².

Scientists call this living community the skin microbiome. Most of its members are harmless or even helpful to the person they live on¹. Learning how they work can change the way you think about soap, showers and the products on your bathroom shelf.

Your skin hosts a busy and mostly friendly neighborhood

For decades, scientists studied skin microbes by growing them in lab dishes. That method only captures the small share of microbes, under 1 in 10, that thrive in standard lab conditions³. Reading microbial DNA straight from skin swabs opened up a far bigger picture.

In 2008, the NIH Common Fund launched the Human Microbiome Project to map the microbes that live on and in healthy people². The project studied 250 healthy volunteers across five body areas, including the skin. At the time, it was the largest study of its kind².

Researchers at NIH’s National Human Genome Research Institute reported that most skin bacteria belong to just four large groups, called phyla¹. Their names are Actinobacteria, Firmicutes, Bacteroidetes and Proteobacteria. Within those four groups, the number of different species is huge¹.

Bacteria share the space with fungi. Yeasts called Malassezia make up about half to four-fifths of the fungi on skin, depending on the spot¹. Microscopic Demodex mites live in hair follicles and their oil glands, most often on the face¹.

Healthy skin is a tough place to settle. It is cool, slightly acidic and dry, which makes it an unwelcoming home for many microbes¹². The surface pH sits around 5, though it varies from one body site to another⁴. The microbes that thrive there are specialists suited to those conditions.

The community also stays fairly steady. The main types of bacteria on your skin tend to stay stable over time, while rarer members come and go³. The inside of the ear, the inside of the nostril and the fold of the groin are among the most consistent spots¹.

New tools keep adding detail. In 2024, researchers at Tokyo University of Science grew four common skin bacteria together in the lab. The mix stayed balanced and resembled communities found on the skin of people in Japan¹³.

Oily, moist and dry skin each host different residents

Your skin works like a map of small climates. The forehead is oily, the armpit is warm and damp, and the forearm is dry and open to the air. NIH researchers found that the body site shapes the skin community more than the person does¹. In fact, your inner elbow has more in common with a stranger’s inner elbow than with other spots on your own body¹.

Oily areas include the face, upper chest, back and the creases behind the ears, where oil glands (sebaceous glands) are plentiful¹. A bacterium that older papers call Propionibacterium acnes, and newer ones call Cutibacterium acnes, rules these sites¹⁹. It breaks down skin oil (sebum) into fatty acids, which help keep the skin surface acidic¹.

Oily sites have the least variety of bacteria. One study counted only six main types on the forehead¹.

Moist areas include the armpit, inner elbow, groin, back of the knee, navel and the spaces between the toes¹. Staphylococcus and Corynebacterium species are the most common residents here¹. These bacteria also process sweat from the armpit glands, which creates the familiar scent of body odor¹.

Dry areas include the inner forearm, the palm near the little finger and the buttock¹. These spots host the widest variety of bacteria, though fewer bacteria overall¹³. Even your two hands differ. In one study, a person’s left and right hands shared only about 1 in 6 of their bacterial types¹.

Your face changes most during the teen years. An MIT study followed 30 children at a Boston-area school and 27 of their parents⁹. The number of bacteria on the face rose about 10,000-fold in the early teens, as hormones ramped up skin oil⁹.

In adults, C. acnes and S. epidermidis together make up about 80 percent of the strains on facial skin⁹. Each person carries up to 11 different lineages of each one⁹. C. acnes strains settle in during the early teens and then stay put⁹. Each S. epidermidis strain, by contrast, lives on the face for less than two years on average⁹.

Skin region	Where you find it	Typical residents	What shapes it
Oily (sebaceous)	Face, upper chest, back, behind the ears	Cutibacterium acnes; Demodex mites in follicles	Skin oil (sebum)
Moist	Armpit, inner elbow, groin, back of knee, navel, between toes	Staphylococcus and Corynebacterium	Warmth, sweat and skin folds
Dry	Inner forearm, palm, buttock	The widest mix of bacteria, in lower numbers	Open air, less oil and sweat
Adult face	Face	C. acnes and S. epidermidis, about 80 percent of strains	Oil output that climbs in the teen years
Most skin sites	Across the body	Malassezia yeasts, about half to four-fifths of skin fungi	Varies by body site

Sources:¹³⁹

Helpful bacteria act like your skin’s security team

Your skin microbes earn their keep. Staphylococcus epidermidis is one of the best studied. In lab research, it makes small proteins called phenol-soluble modulins that hold back harmful germs such as Staphylococcus aureus and Group A Streptococcus¹.

S. epidermidis also signals your skin cells (keratinocytes) to make their own antimicrobial peptides, the body’s built-in germ-fighting molecules¹. Researchers have shown that it can keep S. aureus from settling in the nose and forming sticky colonies called biofilms². NIH scientists describe this body of work as a clear link between friendly skin microbes and the body’s first line of defense¹.

Friendly microbes also help train your immune system. Researchers think skin microbes may help educate the billions of immune cells, called T cells, that live in your skin¹.

Your residents even keep each other in balance. In lab work, an acid made by S. epidermidis (succinic acid) held back the growth of C. acnes³. In similar lab work, C. acnes fermented glycerol in a way that held back S. aureus³.

A team at the University of California San Diego, led by Richard Gallo, took this idea further. They screened about 10,000 bacterial colonies collected from the skin’s outer layer⁶. Most of the 2,029 colonies of coagulase-negative staphylococci (CoNS) collected from 30 healthy people could hold back S. aureus⁵. Among 5,695 colonies from 49 people with eczema (atopic dermatitis), protective colonies were much less common⁵.

One strain, Staphylococcus hominis A9, made two previously unknown antimicrobial peptides⁵. These belong to a family of natural compounds called lantibiotics.

Next, the team grew each volunteer’s own protective bacteria and mixed them into a moisturizing lotion⁵⁶. Five volunteers with eczema received a single dose on one forearm and a plain lotion on the other⁵. Twenty-four hours later, the forearm that got the bacteria carried less S. aureus⁵. Gallo noted that people with eczema may need to reapply such bacteria, because their skin does not naturally favor these helpful strains⁶.

Scientists are testing friendly bacteria on eczema-prone skin

Eczema gives a clear view of what happens when the skin community shifts. More than 90 percent of people with eczema carry S. aureus on their skin, compared with fewer than 5 percent of healthy people¹. During flares, S. aureus becomes more common and overall bacterial variety drops³. Researchers are still working out whether these shifts come before flares or follow them³.

In 2012, NIH researchers noted that eczema had doubled or tripled in industrialized countries over the previous three decades². They list modern hygiene habits and wider antibiotic use among the possible contributors, alongside many other factors².

Scientists at NIH’s National Institute of Allergy and Infectious Diseases (NIAID) took an inventive approach: borrowing helpful bacteria from healthy skin. In lab dishes and mice, a bacterium called Roseomonas mucosa taken from healthy volunteers improved eczema-like signs⁷. Versions taken from people with eczema made those signs worse⁷.

In 2018, the team reported its first human study, led by Ian Myles⁷⁸. Ten adults sprayed a sugar-water mix containing live R. mucosa on their inner elbows and one other area⁸. They did this twice a week for six weeks⁸. The adults kept up their usual eczema care, including steroid creams⁸.

Five children ages 9 to 14 used the spray on all affected areas⁸. They applied it twice a week for 12 weeks, then every other day for four more weeks⁸. Six of the 10 adults and four of the five children saw their eczema severity improve by more than half⁸. Several volunteers needed less steroid cream, and the children carried less S. aureus⁸. No one reported side effects or complications⁷⁸.

This was an early, small study without a placebo group, and the NIAID team called for larger placebo-controlled trials⁸. Bacteria-based approaches like this one are studied as medical therapies, under careful supervision and alongside standard care.

Gentle washing helps your skin’s community stay steady

Daily habits change the conditions your microbes live in. NIH researchers list hand washing, soaps, cosmetics and moisturizers among the factors that alter the skin barrier¹. Scientists are still mapping how these products affect skin microbes over the long run¹.

Small habits leave a mark. In one study, the bacteria on people’s palms shifted depending on how long it had been since they last washed their hands². Two NIH researchers, Heidi Kong and Julia Segre, summed up the modern puzzle well. “Our current society paradoxically strives to colonize our guts with probiotic yogurts, but sterilize our skin with hand sanitizers,” they wrote².

Clean hands still matter for everyday hygiene. Gentle care simply means cleaning your skin without stripping away the cool, slightly acidic surface that your residents are built for¹. The skin’s own oils help keep that surface acidic¹. A routine that leaves some of that oil in place works in harmony with your microbes.

The American Academy of Dermatology (AAD) offers simple advice that fits this goal. Keep baths and showers to 5 to 10 minutes and use warm water¹⁰. Wash with a gentle cleanser, using enough to remove dirt and oil but not so much that you see a thick lather¹⁰.

The AAD also suggests products labeled fragrance-free, and notes that some deodorant soaps are too harsh for dry, sensitive skin¹⁰. Pat your skin dry with a clean towel, then apply moisturizer while your skin is still damp¹⁰. Ointments and creams add more moisture than lotions¹⁰.

Your face needs an even lighter touch. The AAD recommends a gentle, non-abrasive cleanser without alcohol, lukewarm water and your fingertips rather than a washcloth or sponge¹¹. Resist the urge to scrub, and limit washing to twice a day and after heavy sweating¹¹.

Probiotics, prebiotics and the gut-skin connection

Probiotics are live microorganisms intended to have health benefits when consumed or applied to the body¹². You can find them in yogurt and other fermented foods, in dietary supplements and in beauty products¹². The most common belong to two groups, Lactobacillus and Bifidobacterium, and different types may have different effects¹².

Prebiotics are the food for those helpful microbes. They are substances that encourage beneficial bacteria to grow³. Researchers are now working to identify the probiotic strains and prebiotic substances that best support skin communities³.

Researchers are also looking inward, at the gut. A 2014 review from the University of Pennsylvania described a possible link between gut microbes and skin³. One idea is that gut bacteria help educate immune cells³. Scientists often call this two-way relationship the gut-skin axis.

Early life offers clues. In infants, lower variety in gut bacteria has been associated with eczema later on³. The same review noted encouraging early evidence from studies of probiotics and prebiotics taken by mouth in children with eczema³. Researchers are building on these results to learn which strains and amounts suit the skin best.

Skin care is starting to borrow these ideas, too. Because skin bacteria create body odor, researchers have suggested deodorants made with probiotics or prebiotics as a future approach³. The MIT team believes the early teen years may be the best window for introducing probiotic strains of C. acnes to the skin⁹. That is when new strains of this bacterium settle on the face⁹.

Smart use of probiotics

A few simple habits help you get the most from probiotic foods and supplements.

• Read the label for the specific types of bacteria, since different types may have different effects¹².

• Look for a third-party quality seal, such as USP Verified, NSF Certified for Sport or ConsumerLab approved.

• Give any new routine 8 to 12 weeks. The cells on your skin’s surface started their trip up from the deepest layer about 4 weeks earlier¹. Changes take a few of these cycles to show.

• Share your full supplement list with your care team so everything works together. This matters most for people with a serious illness or a weakened immune system¹². For premature babies, let the care team guide every choice¹².

Your surroundings shape your skin’s residents

Your skin community also reflects the life you lead. Warm, humid conditions favor larger numbers of bacteria, and work, clothing and antibiotic use all play a part¹. Geography and lifestyle shape the mix as well³.

The story starts at birth. Babies born vaginally pick up communities that resemble their mother’s vaginal microbes². Babies born by cesarean section first carry communities more like those found on skin². From there, skin communities grow more diverse as children get older².

Variety appears to be a good sign. Diversity can be an advantage in any ecosystem, and low diversity has been linked with some skin conditions³. Everyday choices that respect your skin’s natural oils, acidity and moisture are a simple way to look after that community.

Here is a checklist of microbiome-friendly habits drawn from the research above.

• Keep showers and baths to 5 to 10 minutes in warm water¹⁰.

• Use a gentle, fragrance-free cleanser, and only enough to lift dirt and oil¹⁰.

• Wash your face with your fingertips and lukewarm water, twice a day and after heavy sweating¹¹.

• Skip scrubs and rough washcloths on your face¹¹.

• Pat dry and moisturize while your skin is still damp¹⁰.

• Enjoy yogurt and other fermented foods that contain live cultures¹².

• If you choose a probiotic supplement, check the label for the specific types it contains¹².

• Give any new skin routine 8 to 12 weeks before you judge it¹.

• Share your full supplement list with your healthcare team¹².

The bottom line

Your skin is a living landscape, home to trillions of microbes that help guard it and train its defenses¹². Most of these residents are friends. They are at home on the cool, slightly acidic surface of healthy skin¹.

Short showers in warm water, mild fragrance-free cleansers and a good moisturizer all support the steady surface your microbes prefer. Yogurt, fermented foods and probiotic supplements add another way to care for the helpful microbes in your gut. Research on the skin side is moving quickly.

Scientists are still mapping this world, from the oily forehead to the dry forearm. Each new study adds to an encouraging picture in which caring for your skin also means caring for the community that lives on it.

Sources

1. Grice EA, Segre JA. The skin microbiome. Nature Reviews Microbiology. 2011. pubmed.ncbi.nlm.nih.gov

2. Kong HH, Segre JA. Skin microbiome: looking back to move forward. Journal of Investigative Dermatology. 2012. pmc.ncbi.nlm.nih.gov

3. Grice EA. The skin microbiome: potential for novel diagnostic and therapeutic approaches to cutaneous disease. Seminars in Cutaneous Medicine and Surgery. 2014. pmc.ncbi.nlm.nih.gov

4. Rosenthal M, Goldberg D, Aiello A, Larson E, Foxman B. Skin microbiota: microbial community structure and its potential association with health and disease. Infection, Genetics and Evolution. 2011. pmc.ncbi.nlm.nih.gov

5. Nakatsuji T, Chen TH, Narala S, et al. Antimicrobials from human skin commensal bacteria protect against Staphylococcus aureus and are deficient in atopic dermatitis. Science Translational Medicine. 2017. escholarship.org

6. University of California San Diego Health Sciences. Transplanting good bacteria to kill staph. ScienceDaily. 2017. sciencedaily.com

7. Myles IA, Earland NJ, Anderson ED, et al. First-in-human topical microbiome transplantation with Roseomonas mucosa for atopic dermatitis. JCI Insight. 2018. insight.jci.org

8. National Institute of Allergy and Infectious Diseases, NIH. Bacteria therapy for eczema shows promise. ScienceDaily. 2018. sciencedaily.com

9. Massachusetts Institute of Technology. Study of facial bacteria could lead to probiotics that promote healthy skin. ScienceDaily. 2025. sciencedaily.com

10. American Academy of Dermatology. Dermatologists’ top tips for relieving dry skin. AAD.org. 2026. aad.org

11. American Academy of Dermatology. Face washing 101. AAD.org. 2026. aad.org

12. National Center for Complementary and Integrative Health. Probiotics: what you need to know. NCCIH. 2019. nccih.nih.gov

13. Tokyo University of Science. Scientists develop breakthrough culture system to unlock secrets of skin microbiome. ScienceDaily. 2024. sciencedaily.com

This article is for general education and is not medical advice. Talk with your healthcare professional about your own health, especially before starting a new supplement if you are pregnant, nursing, taking medicine, or managing a health condition. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Reviewed October 2026.