The microbiome, along with its effects on health and wellbeing, is a hot topic across many areas of medicine today, including dermatology. There are still more questions than answers when it comes to how the skin’s bacterial diversity affects eczema risk, but the science is evolving quickly, according to Peter Lio, MD, a Clinical Assistant Professor of Dermatology and Pediatrics at Northwestern University Feinberg School of Medicine and a member of the Board of Directors and Scientific Advisory Committee Member of the National Eczema Association.

What do we know about the relationship between the skin microbiome and eczema?

Peter Lio, MD: We continue to learn more about this relationship at what seems like an ever-increasing pace, with numerous studies, publications, and products rapidly appearing. In more recent history, I would say the thinking was that Staphylococcus aureus was a colonizer and an opportunist. It found the open, oozing skin of atopic dermatitis (AD) an apt home. However, we are learning that Staph may be a primary driver of skin disease for at least some patients, and this is altering our therapeutic approach, at least on the cutting edge. Dr. Heidi Kong at the National Institutes of Health wrote a bold and impressive paper in 2012 that outlined this relationship between the microbiome and AD flares. In short, it suggested that as Staph became more dominant, the microbiome diversity decreased, and this led to a flare. For recovery, the diversity increased again with Staph correspondingly reduced, and then skin symptoms improved. There is a bit of a chicken-and-egg problem here, but I am convinced that Staph overgrowth (and loss of the erstwhile microbial diversity) can be a true cause of disease flares in some instances.

Are there good guys and bad guys?

Dr. Lio: I feel very confident in saying that Staphylococcus aureus is the bad guy here: it dominates, makes a multitude of toxins, and seems to have a verifiable effect on driving AD. The good bacteria are a lot more complex. I think the most timeless answer, perhaps, would be to say that a strong diversity seems to reflect a healthy microbiome and this may well trump identifying one or several species.

Is this something that may be altered in the skin’s microbiome early on that paves the way for newborn eczema?

Dr. Lio: I don’t think we really know for sure, but it certainly seems reasonable and likely. We know that gut microbial diversity in the first week of life is a strong predictive factor for developing AD, and decreased diversity correlates with increased AD risk. We also know that skin barrier dysfunction is an important independent risk factor for developing AD, such as filaggrin mutation and consequent filaggrin deficiency. Thus, it follows that there are very likely to be microbiome abnormalities in newborn eczema, and perhaps if righted early enough, the disease could be halted.

What questions remain about the relationship between the skin microbiome and eczema?

Dr. Lio: There are many questions that need to be answered including the role of birth and home environment on the microbiome, better understanding differences in different body areas, better understanding of pre-biotics and post-biotics beyond just the organisms present. I would say we are at the very beginning here and far from being able to understand how to manipulate the skin’s microbiome for therapeutic purposes at this point.

What probiotics are effective for AD?

Dr. Lio: Midway through 2019, I’m not comfortable saying that any are reliably effective, but there are some studies that suggest oral Lactobacillus GG can have both a protective effect against developing AD and may have a slight (and variable) effect on existing AD. There are several promising topical probiotics on the market, but I don’t feel we have seen enough data yet to routinely recommend them beyond personal explorations. A so-called “microbiome transplant” with Roseomonas was recently published and seemed relatively convincing for an effect on AD severity, but again, much more work needs to be done here before we can confidently recommend such an approach.

Are patients aware of the microbiome and its relationship to AD?

Dr. Lio: Yes, I think there is increasing awareness from patients and families that this may be an important aspect of the disease. Independent innovators such as Dr. Richard Aron have also moved the field forward in this regard, sometimes to the chagrin of the traditional standard-bearers, but as Schopenhauer has written: “All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.”

How are the gut and skin microbiomes intertwined?

Dr. Lio: If we trace the skin around the lips, it becomes the lining of the digestive tract. Indeed, this epithelium has much in common, and the skin and gut both must protect us from the outside world. It seems likely from some small studies that when the skin barrier is impaired, so is the gut barrier. This concept, sometimes called “leaky gut,” appears to correlate with the severity of AD. Beyond these broad strokes of correlation, I sadly don’t think we have much more to say on this topic yet—but there is incredible interest here which will hopefully spur further research in this area.