If you scratch the surface of your skin, you will discover a vibrant community of bacteria living there.
This is actually a good thing, as more and more research shows that the presence of the "right" types of microbes can help skin stay young, elastic, and smooth for longer.
The very presence of "good bacteria" protects us from infections caused by pathogens, harmful microorganisms.
They also help with wound healing and can even mitigate some of the harmful effects of UV radiation.
That's why it's even more important to take care of our skin microbiome.
What should we do?
One method that has become increasingly popular in recent years is applying probiotics to the skin, which in practice means applying live microorganisms directly to the surface of the skin to improve its health.
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As early as 1912, scientists were rubbing bacteria on people's faces in an attempt to improve conditions such as acne and seborrhea, a common form of dermatitis that causes redness, itching, and white or yellow flakes.
Today, there are dozens of skin care companies selling what they call probiotic products, from serums to cleansers and moisturizers.
Each of these products promises to create a “balance” in the skin’s sensitive microbiome and to “renew” and “refresh.”
However, although the labels of many skin care products claim to be probiotics, very few, if any, actually contain live bacteria.
Additionally, because probiotic treatments are classified as cosmetics, not drugs, manufacturers are not required to publish the results of the tests conducted on their products, making it difficult to know how effective they are.
“The rules for skin care products are very different from those for drugs, so claims can be made without the extremely rigorous testing required for pharmaceutical products,” says dermatologist Richard Gallo of the University of California, San Diego School of Medicine, in the United States (US).
Most skin care products advertised as “probiotic” actually contain prebiotics, nutrients that provide the right environment for good bacteria to grow on the skin, or postbiotics, proteins and other compounds that are a byproduct of the fermentation of beneficial probiotic bacteria.
“We are increasingly seeing approaches that try to influence the skin microbiome,” says Bernhard Pecold, co-founder and chief scientific officer of S-Biomedic, a company that tries to treat skin conditions by restoring the microbiome through so-called bacterial “transplantation.”
Pecold explains that the main reason for this approach is that it is extremely difficult to preserve live bacteria during the production, storage and distribution processes.
And even when they do reach the skin, there is no guarantee that they will "take hold", because they have to deal with millions of other microbes that already live there.
The approach to maintaining a healthy skin microbiome is based on the theory that bacteria and fungi that live on the outer surface of the body help protect us from those that could harm us.
However, science has not yet fully clarified how certain "bad" bacteria contribute to the development of skin diseases.
What we do know is that people who suffer from eczema, rosacea, acne, or psoriasis all have different types or amounts of certain bacteria on their skin compared to healthy people.
"What we have right now is a large body of scientific work showing that almost every skin disease we can imagine has some connection to changes in the skin microbiome," says Pecold.
"But this observation only shows an association, it doesn't mean that the change in the microbiome causes the disease."
"It is also possible that the disease itself changes the conditions on the skin and that the bacterial population changes as a result."
To prove that a certain strain of bacteria causes a disease, it is necessary to either cause that disease in a healthy person by applying "bad" bacteria to the skin, or to cure the disease by applying "good" bacteria.
The first option would of course raise serious ethical questions, but several researchers are trying to explore the second option.
However, the limited number of clinical trials published so far show promising results.
Most of them deal with the use of live bacteria to treat eczema, also known as atopic dermatitis.
This research relies on the discovery that the skin of people suffering from eczema is mainly inhabited by Staphylococcus aureus (golden staphylococcus), a bacterium that often has pathogenic properties.
"One of the biggest problems with diseases like eczema is that certain pathogenic bacteria, such as Staphylococcus aureus, colonize the skin surface and cause rashes, disease, and infections," says Gallo, whose team has been investigating ways for years to harness the skin's microbiome to combat harmful bacteria in eczema patients.
"By looking for bacteria that can produce something that eliminates harmful ones, we got types of bacteria that normally live on healthy skin."
Gallo and his team are focused on Staphylococcus epidermidis, a bacteria that is naturally present on the skin and is present in about 21 percent of healthy people, but only one percent of those suffering from atopic dermatitis.
"Our skin provides commensal (beneficial) bacteria like Staphylococcus hominis with a safe place to live, so some of them have evolved a way to protect their environment from harmful bacteria that try to invade," explains Gallo.
The bacterium Staphylococcus hominis produces antimicrobial (defensive) peptides, small pieces of protein that directly kill bacteria. Staphylococcus aureus.
It also produces chemicals that prevent bacteria from communicating with each other.
Some bacteria, such as Staphylococcus aureus, they "communicate" with each other when their population reaches a certain density.
This mechanism is known as quorum sensing (a method of communication between bacteria of the same or different species through signaling molecules) and triggers the secretion of toxins that can cause skin inflammation.
Disabling this communication can prevent the release of toxins.
In 2021, Gallo's team conducted a phase I randomized controlled trial, during which 54 adults suffering from atopic dermatitis applied a cream containing live bacteria for a week. Staphylococcus epidermidis.
The results showed that treatment with this bacteria significantly reduced the presence of Staphylococcus aureus on the skin, and a subgroup of patients experienced a reduction in redness and itching associated with atopic dermatitis, compared to a control group that used a placebo cream.
These findings suggest that a specific composition of bacteria may contribute to a healthier skin microbiome.
However, additional research is needed to confirm the effectiveness of this treatment before it can be used as standard therapy.
The team is now recruiting volunteers for a phase 14 randomized trial that will last XNUMX weeks and is intended to assess the long-term effectiveness of the therapy.
Other researchers have also had success treating eczema with probiotics.
In a 2003 clinical trial, 11 patients with atopic dermatitis applied a cream containing the bacteria for two weeks. Streptococcus thermophilus.
The results showed that the cream stimulated the production of ceramides in the skin, lipid molecules that help hydrate and maintain a healthy skin barrier.
In a more recent study from 2018, 10 adults and five children suffering from atopic dermatitis received a so-called “microbiota transplant,” meaning that live Roseomonas mucosa bacteria, collected from the skin of healthy volunteers, were applied to the patients’ skin twice a week.
After 16 weeks, symptoms improved by more than 50 percent.
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Although there aren't many clinical trials looking at other skin conditions, they also show promising results.
For example, acne is associated with the development of a population of bacteria cutibacterium acnes (formerly known as Propionibacterium acnes).
Therefore, some researchers are looking for bacteria that produce antimicrobial peptides capable of preventing this bacterium from colonizing or eliminating it.
In one clinical trial, patients with severe acne used a lotion containing the bacteria Enterococcus faecalis.
The lotion significantly reduced the number of abscesses compared to the placebo treatment.
In 2019, Pecold and his company S-Biomedic published the results of a clinical trial in which they gave acne patients a cream containing specific strains of bacteria. cutibacterium acnes.
The cream alleviated the acne condition.
Gallo is also investigating whether a particular strain of bacteria Staphylococcus aureus can be an effective treatment for acne.
Animal studies have shown promising results.
"The basic mechanism of action is very simple - preventing the growth of bacteria." cutibacterium acnes similar to what oral or topical antibiotics do to treat acne,” explains Gallo.
Unlike antibiotics applied to the skin, this treatment targets only the bacteria. cutibacterium acnes, so it doesn't affect the rest of the skin microbiome, he says.
Gallo's team even found a special strain of bacteria Staphylococcus epidermidis which produces molecules believed to be able to prevent skin cancer caused by sunlight.
"This bacterium produces a small molecule that prevents DNA synthesis in transformed or mutated skin cells," says Gallo.
"We found that when these bacteria are present on the skin of mice exposed to UV radiation, they develop significantly fewer skin tumors compared to mice that have the same strain of bacteria but without the gene responsible for producing this antimetabolite."
Of course, much more testing and clinical trials of this treatment are needed before it can be determined whether it works in humans.
Although most studies focus on treating specific diseases with probiotics, there are also several studies that have examined whether prebiotics or postbiotics can improve skin health.
For example, some researchers are examining whether inulin, a plant fiber often found in cosmetics and personal care products, can act as a prebiotic when taken orally or applied directly to the skin.
Preliminary results show that inulin can make the skin smoother and more elastic, creating a more favorable environment for the development of beneficial bacteria.
Other studies have shown that administering sphingomyelin phosphodiesterase, an enzyme produced by bacteria like Staphylococcus thermophilus that are common in fermented dairy products and yogurt, can boost the production of ceramides, which are crucial for skin health.
However, to confirm the effectiveness of these creams, large, randomized, double-blind clinical trials, which are the gold standard in medical research, are necessary.
For example, a recent review of studies analyzed all available data from clinical trials conducted to date and concluded that, although “oral and topical probiotics are effective in treating certain inflammatory skin diseases and show promise for wound healing and skin cancer prevention, further research is needed to confirm these results.”
Gallo agrees that more work is needed, but is optimistic about the future of the field.
"We are moving in the right direction," he says.
"As a scientific community, we've realized that we need to understand exactly what probiotics do, and a lot of effort is being put into researching that, as well as creating microorganisms that will benefit us."
"That's why I'm very optimistic about the application of probiotics in a few years."
However, for people who do not have a skin condition but want smoother skin, prevent wrinkles, or improve hydration, there is currently not enough evidence for the effectiveness of probiotics in creams that can be purchased in stores.
“I think there's not enough strong evidence for many of the probiotics currently available on the market, so I wouldn't necessarily recommend them,” says Gallo.
"You can try them, but it might not be the best way to spend your money."
Although the skin microbiome changes as you age and are exposed to various external influences, there are several things you can do to improve your skin's natural microbiome.
"It's a two-way street, because what we already do, like hydrating the skin or protecting it from UV radiation, actually creates an environment that is more suitable for these beneficial microorganisms to live in," explains Gallo.
"So, regular skin care, proper hydration and cleansing - all contribute to skin health."
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