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In a nutshell
- Your skin bacteria aren’t permanent residents—S. epidermidis strains typically last only about 2 years before being replaced, while C. acnes strains are more stable once established.
- Adolescence is a critical window for bacterial colonization—during puberty, C. acnes populations explode by 10,000-fold, potentially creating an opportunity for establishing beneficial strains.
- Family members maintain unique facial bacterial communities despite living in close proximity, sharing only some strains—suggesting personalized approaches may be needed for skin treatments.
CAMBRIDGE, Mass. — Look in the mirror. That face staring back at you isn’t just you—it’s home to billions of microscopic bacteria living in a complex ecosystem. And according to new research, these tiny residents aren’t as permanent as scientists once thought.
A study by researchers at MIT shows that while the same bacterial species dominate our facial skin throughout life, the specific strains within those species are constantly changing—moving in, settling down, and eventually being replaced by newcomers.
Microbiome Musical Chairs
The study, published in Cell Host & Microbe, examined the skin microbiomes of 57 people between the ages of 5 and 60 from 20 different families. They focused on two dominant bacterial species found on nearly everyone’s face: Cutibacterium acnes (which thrives in oily environments) and Staphylococcus epidermidis (which lives primarily on the skin’s surface).
Data revealed striking differences between these two bacterial species. S. epidermidis strains typically last only about two years before being replaced—a much shorter residence than previously known. In contrast, C. acnes strains establish more permanent communities once they move in.
Family members, despite living in close proximity, maintain unique facial bacterial communities. When bacterial strains do transfer between people, it typically involves multiple bacterial cells rather than just one, with parents usually being the donors in these transmission events.
Puberty: The Critical Window for Bacterial Colonization
One of the most remarkable findings centers on adolescence as a pivotal period for bacterial establishment. During puberty, when oil production increases, the population of C. acnes explodes—growing more than 10,000-fold per square centimeter of skin This, of course, explains why pimples become so prevalent during the tween and teen years for many.
Senior author Tami Lieberman notes that C. acnes strains show a pattern of rapid colonization during this time, establishing communities that often persist into adulthood. They suggest this adolescent transition represents a previously unrecognized “window of opportunity” for bacterial colonization that may rival birth and infancy in importance for establishing our microbiome.
It’s why she believes it may be the best time to introduce probiotic strains that could stop breakouts before they happen.
“We found that there are some surprising dynamics, and these dynamics provide insights for how to design probiotic therapy,” says Lieberman, an associate professor of civil and environmental engineering, in a statement. “If we had a strain that we knew could prevent acne, these results would suggest we should make sure we apply them early during the transition to adulthood, to really get them to engraft.”
Although C. acnes has been implicated in the development of acne, it’s still unclear exactly why acne develops in some people but not others. “It may be that some strains are more likely to cause skin inflammation, or there may be differences in how the host immune system responds to the bacteria,” Lieberman explains.
Implications for Skin Treatment and Health
The findings could revolutionize how we treat common skin conditions. Current approaches often involve antibiotics that disrupt the entire microbial ecosystem. Future treatments might instead introduce beneficial bacterial strains during key windows when the skin is most receptive to colonization.
For instance, acne treatments might prove more effective if applied during adolescence when C. acnes strains are actively establishing themselves. And treatments based on S. epidermidis might require more frequent application given the natural turnover of strains every couple of years.
For adults experiencing skin changes every few years, your body might simply be undergoing a natural bacterial transition. Consider tracking changes in your skin’s appearance and sensitivity over time—they might signal shifts in your microbial community. If you’re battling persistent skin problems, discuss with your doctor whether treatment timing might matter.
Parents of pre-teens might want to discuss this research with pediatricians or dermatologists to prepare for the microbial shifts of adolescence. For teenagers especially, the study hints at a golden opportunity during puberty to establish healthy skin bacteria for years to come.
By staying informed about your skin’s invisible residents, you become a better steward of your body’s largest organ and its microscopic inhabitants.
Paper Summary
Methodology
The researchers studied facial skin microbiomes by collecting swab samples from four facial sites (forehead, nose, cheek, and chin) of 57 people aged 5-60 years from 20 different families. They took repeated samples over 1.4 years. For bacterial strain analysis, they cultured 4,055 bacterial isolates, obtaining whole genomes to identify specific strains or “lineages” of C. acnes and S. epidermidis. They also performed metagenomic sequencing (analyzing all DNA in a sample) to detect bacterial presence even when culturing wasn’t possible. The researchers clustered bacterial isolates into 167 distinct lineages based on genetic similarity, then analyzed how these lineages persisted, disappeared, or were transmitted between individuals over time.
Results
The researchers found dramatic differences in stability between the two main facial bacterial species. S. epidermidis strains typically persisted for only about 2 years before being replaced, while C. acnes strains were more stable once established. C. acnes strains colonized most readily during adolescence when facial oil production increases and bacterial density grows 10,000-fold. Despite living in close proximity, family members maintained unique bacterial communities, sharing only some strains. When transmission occurred between individuals, it typically involved multiple bacterial cells rather than just one. Parents were usually the donors in transmission events. The study also identified adolescence as a critical period for microbiome formation, potentially as important as birth and infancy for establishing bacterial communities.
Limitations
The study had a modest sample size (57 individuals) and was conducted over a relatively short period (1.4 years), which may limit the ability to observe longer-term patterns. Sampling was opportunistic rather than systematic, meaning not all family members were sampled at the same time points. The researchers note they couldn’t determine if strains that appeared to be lost from facial skin might persist on other body sites. Additionally, the study couldn’t fully determine the mechanisms behind selective strain sharing between family members or the reasons for different stability patterns between the two bacterial species.
Funding/Disclosures
The research was funded by a pilot grant from the MIT Center for Microbiome Informatics and Therapeutics, a Smith Family Foundation Award for Excellence in Biomedical Research, and NIH grant 1DP2GM140922 to Tami Lieberman. The authors declared no competing interests.
Publication Information
The paper titled “Intraspecies dynamics underlie the apparent stability of two important skin microbiome species” was published in Cell Host & Microbe on May 14, 2025. The authors are Jacob S. Baker, Evan Qu, Christopher P. Mancuso, A. Delphine Tripp, Arolyn Conwill, and Tami D. Lieberman from the Institute for Medical Engineering and Sciences and Department of Civil and Environmental Engineering at Massachusetts Institute of Technology, with additional affiliations at Harvard University, the Broad Institute, and the Ragon Institute.
