What does it really mean to have a balanced microbiome?

What does it really mean to have a balanced microbiome?

We seem to be living in a golden age of skincare, with exciting new products, many of which are backed by today’s hottest celebrities, hitting the market practically every day. These, of course, all come with an array of impressive-sounding claims that are carefully crafted to entice new customers into clicking the ‘buy now’ button, in the hopes that this product will be the one to transform their skin for the better. Amid this endless stream of products and promises, one phrase that you wouldn’t have heard even a few years ago, but suddenly seems to be popping up everywhere, is the claim that a product will help to ‘balance the microbiome’. This sounds pretty amazing—I mean, who doesn’t need a little more balance in their life? But what does ‘balancing the microbiome’ really mean, and is there evidence that skincare ingredients can actually do this? 

Before we dive into these questions, it’s important to understand what we mean when we talk about the ‘skin microbiome’. The skin microbiome refers to the complex ecosystem of tiny microbes that live on, and in, our skin. These include hundreds of different species of bacteria, fungi, and viruses, which are invisible to the naked eye but incredibly important for optimal skin health. The skin microbiome does everything from helping to maintain the skin’s barrier function (basically it’s ability to keep good stuff like water in and bad stuff out) to promoting immune function and protecting from infection caused by pathogenic bacteria and viruses...so it’s kind of a big deal.

The precise make-up of the skin microbiome is unique for everyone, however, there are some key groups of microbes that are typically found on everyone’s skin. These include three kinds of bacteria known as Staphylococcus, Corynebacterium, and Cutibacterium. Within these three groups, there are lots of different species, some of which are beneficial and some that are harmful. For example, beneficial strains of the skin bacterium Cutibacterium acnes, which lives deep within our pores, produce acids that help to keep our skin at an optimal pH of around pH 5.5 and protect from pathogen invasion. However, other more harmful strains of C. acnes produce tissue-damaging molecules and cause blemishes, breakouts, and inflammation. 

All this means that it is incredibly important to have the right combination of  ‘good’ microbes on our skin, while minimizing the harmful ones —what we refer to as having a ‘balanced microbiome’. So getting back to the claim that skincare can balance the microbiome, for this to be true, a product should help to get rid of the bad bacteria and promote growth of good, healthy bacteria. However, when you look at the ingredient list for many of these products, there are few ingredients that actually have these activities. At best, you might find certain ‘prebiotics’ (e.g., galacto-oligosaccharide sugars) that may help to feed the good bacteria on your skin, but there’s little evidence that these can really help to balance your microbiome over time. One recent research study did report that topical use of these prebiotics can improve certain skin parameters and reduce S. aureus bacteria, however, the high concentration used (7%) is far above what is likely to be found in most skincare products. Similarly, there are lots of plant compounds that claim to ‘protect’ the microbiome, but again, it’s not clear what their mechanism is for “protecting” the microbiome, and how effective these are. 

At Ellis Day Skin Science, we have taken an entirely different approach to designing products that balance the skin microbiome. Specifically, we have incorporated skin-native microbes known as bacteriophages (phages for short) in our Balancing Phage Serum and Hydrating Phage Serum, as well as in our brand new Chill Face Spray. These phages target and kill the breakout- and inflammation-causing bacteria that live on skin, which, in turn, helps the good bacteria to grow and flourish….giving you a truly balanced skin microbiome!

Navigating the world of skincare claims, particularly relating to the skin microbiome, can be a challenge for even the savviest consumer, but Let’s Be ClearTM: at Ellis Day Skin Science, we will always be honest with you about how our products work and how they can benefit your skin. As scientists ourselves, we also know that our scientific understanding of the world, especially of something as complex and intricate as the skin microbiome, is continually evolving. There is a lot that all companies and researchers still don’t know. So as new discoveries are made, we will bring those to you and use only the most up-to-date research to help you find the best products for your skin and the trillions of microbes that call it home. 

If you have any questions about the skin microbiome, Ellis Day Skin Science, or how our skin-native products can help to promote skin health, please email us at hello@ellisdayskinscience.com. We’re happy to help!



  1. Barnard E, Shi B, Kang D, Craft N, Li H. The balance of metagenomic elements shapes the skin microbiome in acne and health. Sci Rep. 2016;6:39491.
  2. Di Lodovico S, Gasparri F, Di Campli E, et al. Prebiotic Combinations Effects on the Colonization of Staphylococcal Skin Strains. Microorganisms. 2020;9(1):37. Published 2020 Dec 24. 
  3. Fitz-Gibbon S, Tomida S, Chiu BH, et al. Propionibacterium acnes strain populations in the human skin microbiome associated with acne. J Invest Dermatol. 2013;133(9):2152-2160.
  4. Hong KB, Hong YH, Jung EY, Jo K, Suh HJ. Changes in the Diversity of Human Skin Microbiota to Cosmetic Serum Containing Prebiotics: Results from a Randomized Controlled Trial. J Pers Med. 2020;10(3):91. Published 2020 Aug 17.
  5. Marinelli LJ, Fitz-Gibbon S, Hayes C, et al. Propionibacterium acnes bacteriophages display limited genetic diversity and broad killing activity against bacterial skin isolates. mBio. 2012;3(5):e00279-12.


Dr. Laura Marinelli is a skincare-obsessed scientist who has spent her entire academic career researching phages and the microbes that live on our skin and make up our skin microbiome. She earned her PhD at the University of Pittsburgh, completed her postdoctoral training at UCLA, and is now living her longtime dream of creating phage-based skincare products to improve skin health with Ellis Day Skin Science. Laura has been a part of the Ellis Day team since 2017 and currently lives in Baltimore, Maryland with her husband, three kids, and two cats. 


About Ellis Day Skin Science

We believe that modern skincare must be grounded in true microbiome science and that the most potent, safe, and effective active ingredients are those that are native to healthy skin. 

At Ellis Day Skin Science, we formulate pioneering skincare products using skin-native active ingredients, for the cleanest, safest and most natural approach to healthy skin. These include bacteriophages that eliminate bacteria associated with inflammation, damage, and aging, and enable good bacteria to flourish. 

We use cutting-edge science to leverage these powerful active ingredients, creating products that are just as kind and conscientious as they are effective, so that everyone can feel empowered with balanced, clear, radiant, and resilient skin.

Search our site

Shopping Cart

Your cart is currently empty.